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JULY 1st
TO JULY 3rd
Ecole Nationale Supérieure de Chimie de Rennes
INVITED SPEAKERSSilke Biermann, France
Peter Blaha, AustriaJacky Even, France
Felix Fernandez-Alonso,UKTsuyoshi Kimura, Japan
Artem R. Oganov, RussiaSantiago Rigamonti, Germany
Gian-Marco Rignanese, BelgiumKristian Sommer Thygesen, Denmark
Myung-Hwan Whangbo, USA
https://icamm2019.sciencesconf.org/
CHAIRSFlorent BoucherChris EwelsRégis GautierXavier Rocquefelte
Posters
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Coevolutionary search for optimal materials
in the space of all possible compounds
Zahed Allahyari1,2 and Artem R. Oganov1.2.3
email: [email protected], phone: +7(916)092-2556 1Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, 3 Nobel St.,
Moscow 143026, Russia2Moscow Institute of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny city, Moscow
Region, 141700, Russian3International Center for Materials Design, Northwestern Polytechnical University,
Xi’an,710072, China
Keywords: Coevolutionary algorithm, evolutionary algorithm, hardness, Mendeleev numbers, multi-objective optimization
Abstract
Over the past decade, evolutionary algorithms, data mining and other methods
showed great success in solving the main problem of theoretical crystallography:
finding the stable structure for a given chemical composition. Here we develop a
method that addresses the central problem of computational materials science:
prediction of material(s), among all possible combinations of all elements, that
possess the best combination of target properties. This non-empirical method
combines our coevolutionary approach with carefully restructured ”Mendelevian”
chemical space, energy filtering, and Pareto optimization to ensure that the predicted
materials have optimal properties and a high chance to be synthesizable.
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Ab initio study of the structural and electronic properties of anti-
fluorite Li2X (X = S and Te) compounds
Brahim Bahloul1, Khatir Babesse2, Azzedine Dekhira2, Dalila Hammoutène2
1 Department of Exact Sciences, Ecole Normale Supérieure of Bou-Saada, 28000
M'sila, Algeria 2 Faculty of Chemistry, Laboratory of Thermo-dynamicsand Molecular Modelisation,
USTHB, 16000 Algiers, Algeria
Keywords: Ab initio calculations, anti-fluorite, electronic properties.
Abstract
The structural and electronic properties of anti-fluorite Li2X (X=S and Te) compounds were
investigated using the density functional theory. The exchange-correlation potential is treated
by the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) and the
local density approximation (LDA) of Teter–Pade (TP).
Our calculated lattice parameters at equilibrium volume are in good agreement with available
experimental data and other theoretical calculations.
The electronic band structures and density of states were obtained. The anti-fluorite Li2S and
Li2Te present an indirect band gap of 3.388 eV and 2.493 eV at equilibrium. The top of the
valence bands reflects the p electronic character for both structures.
References
1 W. Kohn, L.J. Sham, Phys. Rev. 140 (1965) A1133.
2 X. Gonze, J. M. Beuken, R. Caracas, F. Detraux, M. Fuchs, G.M. Rignanese, L.
Sindic, M. Verstraete, G. Zerah, F. Jollet, M. Torrent, A. Roy, M. Mikami, Ph. Ghosez, J.Y. Raty, and D.C. Allan, Comput. Mater. Sci. 25 (2002) 478. 3 S. Goedecker, (SIAM) Soc. Ind. Appl. Math. J. Sci. Stat. Comput. 18 (1997) 1605.
4 M. C. Payne, M. P. Teter, D. C. Allan, T. A. Arias and J. D. Joannopoulos, Rev. Mod. Phys. 64
(1992) 1045.
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Investigation of solid phase transitions
considering changes in topology
Viktoriia Baibakova 1,2 , 141700, Dolgoprudny, st. Institutskiy per., h.9, Moscow Region,Russia, [email protected], +7(926)887-91-47
Artem Samtsevich1, 121205, Moscow, st. Bolshoy bulvar, h.30/1, Russia Artem Oganov1,2,3, 121205, Moscow, st. Bolshoy bulvar, h.30/1, Russia
1. Skolkovo Institute of Science and Technology, Moscow, Russia2. Moscow Institute of Physics and Technology, Moscow, Russia
3. Northwestern Polytechnical University, Xian, China
Keywords: materials science, computational chemistry, rare events
Abstract
Huge temperature and pressure in Earth mantle induce several processes to take
place. Among them there are rare reaction events of transitions from one solid phase
to another. Thus, perovskite (brigmanite) structure degradates to post-perovskite;
quartz reaches new phases through a chain of transitions to coesite and then to
stishovite1. These processes are under investigated now, which makes them to be
the hottest topic in Computational Chemistry. Mathematically, the problem of
modeling phase transition path can be rephrased as locating the Minimal Energy
Pathway on Potential energy landscape2. Existing approaches, for instance, the most
abundant Nudged Elastic Band3 method, can deal with only the simple cases with
small number of atoms in a unit cell, and the events, described above, are out of
reach for them. Under this motion, our group proposes a new two steps algorithm for
the calculation of the transition pathway in case of solids.
Firstly, atoms are matched after consideration of the topology or after the geometrical
search. For all the transitions the topological4 matching of atoms between the initial
and the final structures has been less time consuming and has demonstrated more
variety in cope with higher reliability of obtained results. Despite of that, the
geometrical approach to the building of the mapping was more effective in the cases
when the two ending structures have too different symmetries. In the latter case the
topological approach performs poor as it requires the determination of a common
group of symmetry, and when it is very low, the number of possible variants
exponentially grows, and the priority shifts to geometrical consideration.
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Secondly, the initial approximation of the transition pathway is built. It can be realized
with a Linear approximation of atomic motion. But the problem of such approach is in
producing result being far away from real transition path. Alternatively, we have
implemented Image Dependent Pair Potential5 Method for the case of solids. It let us
to get a model, representing physics and chemistry of the transition. Some simpler
cases demonstrated the accuracy of algorithm, for instance transition rutile- anatase
(SiO2) and CrN systems. Consequently, it has sped up the calculation of complex
transitions several times.
References
1Spray J., Boonsue S. Quartz-coesite-stishovite relations in shocked metaquartzites from the Vredefortimpact structure, South Africa // Meteoritics & Planetary Science. 2017. Т. 53. № 1. С. 93-109.2Henkelman G. Atomistic Simulations of Activated Processes in Materials // Annual Review of Materials Research. 2017. Т. 47. № 1. С. 199-216.3Xiao P. et al. Solid-state dimer method for calculating solid-solid phase transitions // The Journal of Chemical Physics. 2014. Т. 140. № 17. С. 174104.4Blatov V., Shevchenko A., Proserpio D. Applied Topological Analysis of Crystal Structures with the Program Package ToposPro // Crystal Growth & Design. 2014. Т. 14. № 7. С. 3576-3586.5Smidstrup S. et al. Improved initial guess for minimum energy path calculations // The Journal of Chemical Physics. 2014. Т. 140. № 21. С. 214106.
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Investigations on double perovskites Pr2MnNiO6 and Nd2-xSrxMnNiO6: Spectroscopy and ab-initio studies
Padmanabhan Balasubramanian
Department of Allied Sciences, Graphic Era University, Dehra Dun, Uttarakhand 248002, India.
Abstract The electronic structure of double perovskite Pr2MnNiO6 was studied using core x-
ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and ab-
initio calculations [1]. Based on charge transfer multiplet analysis of the Ni/Mn 2p
XPS and XAS spectra, we find charge transfer energies of 3.5 and 2.5 eV for Ni and
Mn respectively. The ground state of Ni2+ and Mn4+ ions reveal a higher d electron
count of 8.21 and 3.38 respectively as compared to the ionic values. The partial
density of states show a charge transfer character of the system for U−J ≥ 2 eV
wherein an increase in U does not change the band gap. With increase in U−J, the
spectral weight of O 2p states increase below EF, while the spectral weights of Ni
and Mn 3d states, become smaller in comparision. The O 1s edge absorption spectra
reveal a band gap of 0.9 eV, which is close to the value estimated from XPS and
XAS. Our studies reveal that the material is a p−d type charge transfer insulator with
an intermediate covalent character as per the to the Zannen–Sawatzy–Allen phase
diagram.
In second part of my talk, I shall discuss effect of Sr doping on Nd2MnNiO6. The
compound Nd2-xSrxMnNiO6 (x=0, 0.2, 0.4, 0.5 and 1) is investigated experimentally
from bulk magnetization, x-ray spectroscopy and ab-initio methods [2]. There occurs
a structural transformation from monoclinic (P21/n, for x = 0 to 0.5) to cubic (for x =
1). The systematic reduction in magnetic moment at 5 K suggests an increase in
antisite disorders with doping. Our GGA-based calculations for the ordered supercell,
predict half metallic character for doping (x > 0) samples due to delocalization of Ni
eg orbitals. The theoretical magnetic moment of Mn remains constant irrespective of
doping, x. However, the moment of Ni shows a drastic reduction with doping, from
1.4 μB to 0.7 μB suggesting an increase in covalent character of the system.
Temperature dependent resistivity measurements exhibit a clear metallic region for x
= 0.2 sample, while for x > 0.2, the metallicity gets suppressed due to increase in
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anti-site disorders. Calculations on supercell with anti-site disorder was
systematically performed with flip of 1 and 2 Mn/Ni sites which yield drastic reduction
in Ni moments. With doping, the disordered anti-ferromagnetic phase yields lowest
energy, especially for x=1.
References
1P. Balasubramanian, S. R. Joshi, R. Yadav, F. M. F. de Groot, A. K. Singh, A. Ray, M. Gupta, A. Singh, S. Maurya, S. Elizabeth, S. Varma, T. Maitra, V. Malik, J. Phys.: Condens. Matter 30, 435603 (2018). 2A. K. Singh, P. Balasubramanian, A. Singh, M. K. Gupta, R. Chandra, J. Phys.: Condens. Matter 30, 355401 (2018).
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On the Electrochemical Catalytic and Molecular Properties of
Nanographene-Pyrazines Conjugated Metal [M=Fe, Ru] Complexes:
Computational Insights
Abdulilah Dawoud Bani-Yaseen, Asia Aboulsoud, Elkhansa Elbashier
Department of Chemistry& Earth Sciences, College of Arts & Sciences, Qatar University
P.O. Box: 2713, Doha, State of Qatar [email protected]; Tel: +974-4403-6546
Keywords: molecular electrocatalysis, graphene, metal complexes, reduction potential, density functional theory
Abstract
Immobilization of metal-based molecular complexes on nanostructured materials has
recently gained great level of interests.1-3 As such, heterogeneous electrocatalysts can
exhibit more efficient performance than the homogeneous analogue in terms of
recoverability and durability. However, it is of great importance to assess the molecular
properties of molecular heterogeneous catalyst to examine the retainability of the
properties of the homogeneous analogue after heterogenization. In this work, the
electrochemical catalytic properties of nanographene-based heterogenized molecular
complexes of the (2,2′-bipyridyl)-metal complex, [M(bpy)3]2+ (M= Fe, Ru) are evaluated
by computational study via DFT method with an implicit solvation model (IEFPCM).
Interestingly, the computational results revealed good agreement between
nanographene-based heterogeneous electrocatalyst, [M(bpy)2]+2-Gr and their
homogeneous analogues in terms of electrochemical and molecular properties in
acetonitrile. Moreover, the redox potential, the optimized geometries, and molecular
orbitals are analysed and properly discussed. Significantly, the findings of this work
may help in designing more efficient nanographene-based molecular heterogeneous
electrocatalysts for wide spectrum of applications including energy conversion and
storage.
References
1L. Liu, A. Corma, Chemical Reviews 118, 4981 (2018). 2C. Costentin, J.-M. Savéant, Nature Reviews Chemistry 1, 0087 (2017). 3S. Hammes-Schiffer, Accounts of Chemical Research 51, 1975 (2018).
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Noncollinear magnetic properties and magnetocaloric effect of the
RMn2Si2 compounds
W. Bazine1,*, N. Tahiri1, O. EL Bounagui2, H. Ez-Zahraouy1 and A. Benyoussef3,4
*e-mail: [email protected], phone: +212670747268 1 Laboratory of Condensed Matter and Interdisciplinary Sciences
Department of Physics, Faculty of Sciences, Mohammed V University P. O. Box 1014, Rabat, Morocco
2Institute of Nano-materials and Nanotechnology, MAScIR, Rabat, Morocco. 3Resident member of a Hassan II Academy of Science and Technology, Rabat, Morocco.
4EPHE, Modeling & Simulations, Faculty of Science, Mohammed V University, Rabat, Morocco
Keywords: Magnetic properties; Magnetocaloric effect; Ab-initio calculation; Noncollinear magnetic; intermetallic; Monte Carlo Simulation; Heisenberg model.
Abstract
In this study, the structural, magnetic, electronic and magnetocaloric properties of the
ternary intermetallic RMn2Si2 compound are presented. The RMn2Si2 compound,
where R is Ca, La, Ba, Y or rare earth, is an important class of materials, which
exhibits a wide variety of interesting physical properties. Depending on the
constituent element or composition, various properties like superconductivity,
magnetic ordering, heavy-Fermi on properties, shows a large variety of collinear and
noncollinear magnetic ground states (GS) depending on R [1-3]. Firstly, We
presented a systematic study of the stability of the collinear and noncollinear
magnetic states for different R atoms. The magnetic and magnetocaloric properties
of this material have been studied using Monte Carlo Simulation (MCs) by adopting
various models, including the Ising model and Heisenberg model. Then, we
calculated the isothermal magnetic entropy change, adiabatic temperature change
and relative cooling power (RCP) for different external magnetic fields. Finally we
gave an overviewer of this type of compound.
References
1 B.Emre, S.Aksoy, O.Posth, M.Acet, E.Duman, J.Lindner and Y.Elerman. J. Physical Review B 78
(2008) 144408. 2 A.Szytuta and J.Leciejewicz. Handbook on the Physics and Chemistry vol 12 chapter 83 (1989) 133-
211. 3 S.Di Napoli, G.Bihlmayer, S. Blugel , M.Alouani, H.Dreysse , A.M. Llois. Journal of Magnetism and
Magnetic Materials 272–276 (2004) e265–e266.
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Studies of the electronic properties of the spinel
compound CuCrSnS4 by DFT
Karima BELAKROUMa, Radia BENECHEIKH
a, aUniversité Kasdi Merbah-Ouargla, department de Physique, Route de Ghardaia, 30000,
Ouargla, Algeria e-mail:[email protected]
Phone number :213552927887 Keywords: Spinel structure, CuCrSnS4, ab initio calculation, structural and electronic properties
Abstract
Inorganic compounds with the AB2X4 spinel structure have been studied for many
years and are in the focus of modern solidstate physics, because of their unusual
physical properties, as there are heavy-fermion behaviour, complex spin order, spin
dimerization, spin–orbital liquid, orbital glass, and multiferroicity1,5. In the
crystallographic spinel structure, first solved by Bragg in 1915, the cations occupy 1/8
of the tetrahedral (A) and 1/2 of the octahedral (B) voids within the face-centred cubic
(fcc)-lattice formed by the X anions. Interesting physics arises, when the B-site
cations become mixed in valence. As the cations show different site preferences, by
choosing the appropriate atoms it is possible to realize a selective magnetic dilution
in one of the two sublattices. Thiospinel CuCr2S4 is well known that the metallic
compound which shows a ferromagnetic transition at a Curie temperature TC=377K2.
The Cr ions in CuCr2S4 are in a mixed valence state with Cr3+ and Cr4+. The
ferromagnetism of this compound is attributed to the double exchange interaction
between Cr3+ and Cr4+ via the conduction electrons. Cu2xCr2xSn2-2xS4 was studied3,4
and was reported to be a cluster spin glass on the basis of the various features
observed in neutron patterns recorded as a function of temperature. We focus on the
corresponding selenide compound CuCrSnS4 to study the influence of the larger S
anions on the crystallographic and magnetic properties by using a theoretical study.
The approach followed in this work is based on the Hohenberg-Kohn density-
functional theory (DFT). Density functional theory (DFT) is frequently used to study
the electronic structure of solids. The choice of exchange-correlation potentials can
affect the results. The linearized augmented plane wave (LAPW) method plus the
use of local orbitals is the basis for the WIEN2k code, that is used to simulate our
materials. This program package is one among the most accurate versions for DFT
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calculations. Exchange and electronic correlation are described by the local density
approximation. To identify the exchange mechanism, which stabilises
ferromagnetism or antiferromagnetism, is an important problem in magnetic
materials. For dilute magnetic semiconductors this means identifying the mechanism
which stabilises the ferromagnetism already for small concentrations. In this paper
we review the latest achievements of density functional theory in understanding the
physics of diluted magnetic semiconductors. We will discuss the basic electronic
structure of dilute magnetic semiconductors, the origin of ferromagnetism in these
materials and presented ab-initio calculations for the electronic and magnetic
properties of CuCrSnS4.
References
1J. Hemberger, P. Lunkenheimer, R. Fichtl, H.-A. Krug von Nidda, V. Tsurkan, A. Loidl, Nature
(London) 434 364. (2005)
2S. Weber, P. Lunkenheimer, R. Fichtl, J. Hemberger, V. Tsurkan, A. Loidl, Ph ysical Review Letters
96 157202 (2006).
3Y. Yamasaki, S. Miyasaka, Y. Kaneko, J.-P. He, T. Arima, Y. Tokura, PhysicalReview Letters 96
207204. (2006)
4T. Rudolf, Ch. Kant, F. Mayr, J. Hemberger, V. Tsurkan, A. Loidl, New Journal of Physics 9 76 (2007).
5J. Hemberger, T. Rudolf, H.-A. Krug von Nidda, F. Mayr, A. Pimenov, V. Tsurkan, A. Loidl, Physical
Review Letters 97 087204 (2006).
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Optoelectronic properties of ZnSiN2 - based solar cells:
First-principles study via modified Becke-Johnson approach.
BENNACER Hamza1, 2,BOUKORTT Abdelkader 2 ,ZIANE Mohamed Issame 2, SaidMeskin2
1-Mohamed Boudiaf university of M’sila, electronics department, 28000 Algeria.2-Elaboration and Characterization Physical Mechanics and Metallurgical of Material,Laboratory, ECP3M, Electrical Engineering Department, University of Mostaganem
27000, Algeria.
Keywords: II-IV-V2 materials, solar cells, DFT, Wien2k, TB-mBJ.
Abstract
The main aspects of interest for a material to be used in optoelectronic: emission of
light and photovoltaic effect. Recently, II-IV-V2 compounds have received much
concentration due to their potential applications in nonlinear optic, and photovoltaic
absorber material in solar cells. The optoelectronic properties of ZnXN2 (X=Si, Ge)
ternaries have been theoretically investigated from first principles. In this work we try
to calculate and to study the optoelectronic properties using FP-LAPW method by the
Wien2k code within TB-mBJ approximation, to detect their competence and ability in
photovoltaic applications.
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Complex Borohydride - Energy Storage and New Advancements
H. Benzidia, M.Gararaa , A. Benyoussef b, A. El kenz a, O. Mounkachia
aLaboratory of Condensed Matter and Interdisciplinary Sciences (LaMCScI), Associated to
CNRST (URAC 12), Physics Department, Faculty of Sciences, Mohammed V University,
Rabat, Morocco
bMaterials and Nanomaterials Center, MAScIR Foundation, Rabat Design Center Rue
Mohamed Al Jazouli Madinat Al Irfane Rabat 10 100 Morocco
Corresponding author: [email protected] (H. Benzidi);
Keywords: First principal calculations; Electronic properties; Complex hydride; Hydrogen
storage; Enthalpy; kinetics
Abstract
Borohydride complexes of alkali and alkaline-earth metals have widely investigated
as a promising material for solid-state hydrogen storage because of their large high
gravimetric and volumetric hydrogen capacities, e.g., lithium borohydride (LiBH4)
have the highest capacities among other solid storing materials 18.3% wt.
Nevertheless, the partial release of hydrogen requires a high pressures and
temperatures (upto 600°K, 10MPa), due to its high thermal stability and unwanted
side reactions such as formation of stable closo-boranes (LiB10H10, Li2B12H12)
leads to a poor reversibility. Which, limits its practical use. To avoid these difficulties,
different techniques are adopted. Our study carried out based on the density
functional theory as implemented in quantum espresso code, featured with some
other packages in order to extract some other properties (vibrational lattice,
thermodynamic properties, transport or optic properties). In order to develop a high-
performance energy storage system based complex borohydride materials.
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First principles study of the electronic structure and electrical properties of
Polymers
Parrydeep Kaur Sachdeva and Chandan Bera Institute of Nano Science and Technology, Habitat Centre,Phase-10,Mohali-160062,Punjab,India
[email protected], +91-7986113782
Keywords: Density functional theory, Polyvinylidene fluoride, Dielectric constant, anisotropic,
non-centrosymmetric, piezoelectric
Abstract
For large range of applications, the electrical properties of semi-crystalline polymers have been
exploited. Among the polymers, Polyvinylidene fluoride (PVDF) having a non-centrosymmetric
structure exhibits great potential in nano-scale energy storage and electromechanical devices.
PVDF is experimentally reported to have high dielectric constant and band gap. It exists in
different phases- α, β, Υ and δ. The electronic structure of β phase of PVDF has been
investigated using density functional theory (DFT). We got the band gap for β phase having
orthorhombic structure to be 4.5 eV at the Г-point using generalized gradient approximation
(GGA). Hybrid functionals give better results for band gap for insulating polymers as compared
to results obtained using GGA and local density approximation (LDA). The difference between
the band structures of different phases of PVDF is caused by the difference in their molecular
conformations and space groups.
The static and frequency dependent dielectric properties of polar form (I) have been analyzed
using density functional perturbation theory (DFPT). An anisotropic dielectric property is
observed from the results of DFPT calculation in crystalline PVDF. The future work aims at
determining the piezoelectric and pyroelectric properties of this polymer. The detailed
investigation of these properties will help in better understanding and hence improving the
power density of energy storage devices to meet the increasing energy demands of society.
Representation of chain segment of β-phase of PVDF
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Bandstructure and DOS of β-phase of PVDF
References
[1] Naoki Karasawa and William A. Goddard, Macromolecules 28, 6765 (1995).
[2] Andrew J. Lovinger, Science 220, 4602 (1983).
[3] R. Gregorio, JR., J. Mater. Sci. 34, 4489 (1999).
[4] Chun-Gang Duan, W. N. Mei, J. R. Hardy, S. Ducharme, Jaewu Choi and P. A. Dowben, Europhys. Lett. 61
(1), 81 (2003).
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FIRST PRINCIPAL CALCULATIONS OF STRUCTURAL ELECTRONIC
AND THERMODYNAMIC PROPERTIES OF PbS1-xTex ternary alloys
N Boukhris, H Meradji, S Ghemid, S Drablia
Laboratoire LPR, Département de Physique, Faculté des Sciences, Université de Annaba, Algeria. Email : [email protected]
Kaywords : DFT, FP-LAPW, thermodynamic properties
Abstract
The structural, electronic and thermodynamic properties of PbS1−xTex ternary alloys have
been calculated using the full-potential linearized-augmented plane wave method. The
exchange and correlation potential is treated by the generalized gradient approximation
(GGA) using the Perdew–Burke–Ernzerhof parameterization.
Moreover, the Engel–Vosko GGA formalism is also applied to optimize the corresponding
potential for band structure calculations. A nonlinear dependence of the effect of the
concentration (x) on the lattice constants, bulk modulus and band gaps is found. The
microscopic origins of the band gap bowing parameter have been discussed. Moreover, the
thermodynamic stability of the studied alloys is investigated by means of the miscibility
critical temperature.
1. Introduction
Lead chalcogenide narrow-gap semiconductors PbX (X =S, Se and Te) and their
alloys have been applied in long-wavelength imaging [1], in diode lasers [2] and in
thermophotovoltaic energy converters [3]. The IV–VI compounds are semiconductors
with a good grade of polarity, with bondings formed through electrostatic interactions
among the ions of the crystal lattice, crystallizing in the rock-salt-type structure.
Compared with the usual III–V compounds, for example, these IV–VI chalcogens
present atypical electronic and transport properties, such as small energy gaps, low
resistivities, large carrier mobilities, narrow band gaps and positive temperature
coefficients [4, 5]. These properties make these compounds particularly useful as
electro-optical devices of 3–30μm wavelength, corresponding to the medium and far
infrared. These known characteristics and unusually high dielectric constants, which
do not appear in polar crystals, have made various electrical and optical
measurements possible, thus allowing a close view of the relationship between the
optical, electrical and chemical properties of polar crystals. The lead salts are of great
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importance in infrared detectors, light-emitting devices and as infrared lasers in fiber
optics, as thermoelectric materials and in window coatings [6–9]. The small energy
gap of lead chalcogenides (PbS, PbSe and PbTe) is one of the most important
properties prompting great experimental interest in these materials. Experimental
research has been performed on their structural and band properties [10, 11].
References
[1] Zogg H, Fach A, John J, Masek J, Muller P, Paglino C and
Buttler W 1994 Opt. Eng. 33 1440
[2] Preier H 1979 Appl. Phys. 20 189
[3] Chaudhuri T K 1992 Int. J. Eng. Res. 16 481
[4] Dalven R, Ehrenreich H, Seitz F and Turnbull D (ed) 1973
Solid State Physics vol 28 (New York: Academic) p 179
[5] Cowley R A 1965 Phil. Mag. 11 673
Murase K 1980 J. Phys. Soc. Japan 49 (Suppl.) 725
[6] See, for example, Agrawal G P and Dutta N K 1993
Semiconductor Lasers (New York: Van Nostrand Reinhold)
p 547
[7] Hicks L D, Harman T C, Sun X and Dresselhaus M S 1996
Phys. Rev. 53 R10493
[8] Chatterjee S and Pal U 1993 Opt. Eng. 32 2923
Chaudhuri T K 1992 Int. J. Energy Res. 16 481
Mohammad M T 1990 Sol. Energy Mater. 20 297
[9] Nair P K, Ocampo M, Fernandez A and Nair M T S 1990 Sol.
Energy Mat. 20 235
Nair P K, Fernandez A and Nair M T S 1989 Proc. SPIE
1149 88
[10] Nimtz G, Schlicht B and Dnhaus B 1983 Narrow Gap
Semi-Conductors (Springer Tracts in Modern Physics)
(New York: Springer)
[11] Miller A, Saunders G and Yogurtcu Y 1981 J. Phys. C: Solid
State Phys. 14 1569
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Stabilizing the perovskite phase of cesium lead iodide thin films
via interfacial strains
T. Braeckevelt1, J. Steele2, K. Lejaeghere1, S.M.J. Rogge1, J. Hofkens3, V. Van Speybroeck1
1Technologiepark 46, 9052 Zwijnaarde, Belgium. [email protected]. Phone: +32 (0)9 264 66 41 (Belgium)
2,3Celestijnenlaan 200F, Leuven, 3001, Belgium 1Center for Molecular Modeling, Ghent University
2Centre for Surface Chemistry and Catalysis, KU Leuven 3Department of Chemistry, KU Leuven
Keywords: Perovskites, solar cells, phase stability, density functional theory, interfacial strain.
Abstract
Metal halide perovskites (MHPs) are a class of materials with excellent photovoltaic
properties. In the last decade, the efficiency of perovskite solar cells has increased
rapidly from 3.8% in 2009 to 23.7% presently. This high efficiency is the result of their
extraordinary properties such as a high absorptivity, long electron-hole diffusion
lengths, and a high charge mobility. Furthermore, MHPs are more versatile, easier to
synthesize, and cheaper to produce than the more traditional absorbing materials in
solar cells. The major hurdle preventing the large-scale commercialization of
perovskite solar cells is their low stability in atmospheric conditions. For example, the
most popular MHP, methylammonium lead iodide (MAPbI3), degrades rapidly when
brought into contact with water.
To increase the perovskite’s stability, the organic MA molecules can be replaced with
less volatile inorganic atoms such as cesium, with CsPbI3 reaching a solar cell
efficiency above 17%. Unfortunately, CsPbI3 is polymorphic. At high temperatures
(~600°C) the CsPbI3 perovskite or black phase is stable. However, at room
temperature, the black phase is only metastable and will eventually transform to the
stable non-perovskite or yellow phase, thereby losing its attractive photovoltaic
properties. To counteract this black-to-yellow phase transition, the stability of the black
phase has been increased experimentally by forming nanocrystals, surface
functionalization, and compositional tuning1. Recently, we have investigated the effect
of depositing a thin CsPbI3 film onto a glass/indium tin oxide (ITO) substrate. The
different expansion coefficients of ITO and CsPbI3 result in an interfacial strain, which
was experimentally demonstrated to increase the stability of the black phase.1
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To understand how this interfacial strain modifies the phase stability of CsPbI3 and
explore how this mechanism may be adopted to stabilize other MHPs, ab initio
simulations were performed with VASP for both the black and the yellow phase, with
and without the experimentally observed interfacial strain. When considering a strained
perovskite thin film, the lateral dimensions stay fixed due to clamping to the substrate,
thereby introducing a biaxial strain in the CsPbI3 thin film. To account for the
polycrystallinity of the perovskite, many different planes were biaxially strained and the
average effect of strain on the energy was determined.
The resulting energy diagram is depicted in pane a of the figure below. Without
interfacial strain, the yellow phase is about 85 meV more stable than the metastable
black phase, resulting in a substantial driving force from the black towards the yellow
phase. However, when applying a biaxial strain, the yellow phase is substantially
destabilized. This decreases the energy difference between both phases to ca. 60
meV, thereby confirming that interfacial strains can be introduced to stabilize the black
phase and slow down the black-to-yellow-phase transition.
References
1J.Steele, H. Jin, I. Dovgaliuk, R. F. Berger, T. Braeckevelt, H. Yuan, C. Martin, K. Lejaeghere, S. M. J. Rogge, C. Notebaert, W. Vandezande, K. Janssen, B. Goderis, E. Debroye, M. Saidaminov, H. Tan, V. Dyadkin, D. Chernyshov, V. Van Speybroeck, E. Sargent, J. Hofkens, M. B. J. Roeffaers, Thermal Stabilization of Strained Black CsPbI3 Thin Films, submitted.
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Ab initio calculations of structural and electronic properties of CaScompound.
Chaouche Yassine1,* and Souadkia Mourad2
1University of Larbi Tebessi, Tebessa, Laboratoire de Physique Appliquée et Théorique,Route de Constantine 12002 Tebessa, Algeria
2Physics Laboratory at Guelma, Faculty of Mathematics, Computing and Material Sciences,University 8 Mai 1945 Guelma, P.O. Box 401 Guelma 24000, Algeria
E-mail address : [email protected]; [email protected] number: 00213554551875
Keywords: GGA (WC), GGA (PBE) , LDA, Structural and electronic properties, immediatelyafter the affiliations, provide a maximum of six keywords (avoid, for example, 'and', 'of'). Noabbreviations used: unless firmly established in the field. 11pt Arial, left justified and singlespaced.
AbstractWe have studied the structural and electronic properties of CaS compound using
recently proposed Wu-Cohen generalized gradient approximation. Our results show
that there is excellent improvement in the structural parameters over the standard
LDA and PBE such as lattice parameter with a= 5.65, 5.72 and 5.57 A° for GGA
(WC), GGA (PBE) and LDA respectively. While the bulk modulus results are : 61.7,
56.6 and 56.6 GPa for GGA (WC), GGA (PBE) and LDA respectively. These results
are in good agreement with available data. The values of the band gap in B1 phase
(Γ–X) 2.15, 2.4 and 1.9 ev for GGA (WC), GGA (PBE) and LDA respectively. The
values also improve quite appreciably as compared to LDA results. The widely
studied B1 phase of CaS appears to have an indirect band gap, which is in
agreement with the experimental studies as well as with some earlier theoretical
calculations. It is shown that the S p states and Ca 3d states play a major role in
optical transitions as initial and final states, respectively.
References1
H. Luo, R.G. Green, K. Ghandehari, T. Li, A.L. Ruoff, Phys. Rev. B 50, 16232 (1994)2
Z. Charifi, H. Baaziz, F. El Haj Hassan, N. Bouarissa, J. Phys.: Condens. Matter 17, 4083 (2005)3
Z.J. Chen, H.Y. Xiaa, X.T. Zua, Physica B 391, 193 (2007)
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sp3 Bonded 2-Dimensional Allotrope of Carbon: A First-Principles
Prediction
Bikram Kumar Das, Dipayan Sen, Kalyan Kumar Chattopadhyay
Email: [email protected], Phone number: +919593415102
Thin Film and NanoScience Laboratory, Department of Physics, Jadavpur University,
Kolkata, 700032, India
Keywords: DFT, Carbon, Phonon, Bandstructure, Strain
Abstract:
2-dimensional allotropes of carbon have lately attracted significant research interests
owing to their unique electronic and structural properties1. Such sp and sp2 bonded
atomic systems, i.e. graphdiyne2 and graphene3 are well represented in the forefront
of theoretical and experimental chemistry. However, any stable sp3 bonded 2-
dimensional all-carbon atomic structure has not been identified yet. To this end,
using state-of-the-art theoretical calculations, we considered cyclobutane motifs, and
investigated whether a sp3 bonded 2-dimensional carbon allotrope could be
achieved by assembling ladderane chains. Energetic and dynamic stability studies
yielded two such promising structures: one with 4-coordinated carbon atoms and a
relatively more stable structure with a combination of 3 and 4-coordinated carbon
atoms; both having puckered geometries and partially sp3 C-C bonds. However
thermal stability investigations indicated only the lower energy configuration could be
stable at ambient temperature and pressure. The higher energy structure was found
to be metastable and was observed to suffer phase-transitions towards the lower
energy structure or other stable 2-dimensional allotropes of carbon under exposure
to ambient conditions. Investigation of electronic properties of these proposed
materials revealed them to be direct-gap semiconductors with small bandgaps. It
was also observed that their bandgaps can be readily tuned by applying external
strain, implying they might be useful from the perspective of microelectronics
applications.
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References
1S. Zhang, J. Zhou, Q. Wang, X. Chen, Y. Kawazoe, and P. Jena, Proceedings of the National
Academy of Sciences 112, 2372 (2015).
2R. Matsuoka, R. Sakamoto, K. Hoshiko, S. Sasaki, H. Masunaga, K. Nagashio, and H. Nishihara,
Journal of the American Chemical Society 139, 3145 (2017).
3K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and
A. A. Firsov, Science 306, 666 (2004).
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Single-atom Catalysis on a Silica Support: A Density Functional Theory study
Xavier Deraet,*Jan Turek, Mercedes Alonso, Frederik Tielens, Frank De Proft *[email protected],+3226293580
Eenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
Keywords: single-atom catalyst, amorphous silica, conceptual density functional theory, periodic density functional theory.
Abstract
Despite the fact that metal-based catalysts have been used for decades, scientists are
still seeking for those catalysts delivering the largest atomic efficiency. This concept is
based on the evidence that the availability of most of the d-metals used in catalytic
processes is rather low and continuously diminishing as well as on the awareness that
most of these processes occur at the metal surface, meaning that any atom that could
not be approached by reactant molecules is wasted. These observations together with
the aim of developing greener catalytic processes has led to the systematic reduction
in the cluster size to the most extreme situation where only single metal atoms are
dispersed on a support, a so-called single-atom catalyst (SAC). However, the stability
and catalytic activity of such a SAC is still highly debated.
The aim of our work consists of systematically reducing the number of metal atoms on
a previously constructed hydroxylated amorphous silica slab1 and analysing changes
in catalytic activity and chemical reactivity within the framework of conceptual and
periodic DFT.
The adsorption energy and corresponding charge transfer for the binding of single
metal atoms of Group 8 (Fe, Ru, Os), Group 9 (Co, Rh, Ir), Group 10 (Ni, Pd, Pt) and
Group 11 (Cu, Ag, Au) on the silica slab was investigated. Our calculations indicate a
decreasing trend in Bader charges when moving down and across the rows from
group 8 to 11 elements, which is in good agreement with the electron affinity of these
elements. In addition, we also observed (Figure 1) that the adsorption energy for
Group 8 to 10 metals increases, with the exception of Pd, when progressing down
these groups. The inert metals are logically less eager to interact with the surface.
Current research consists of calculating conceptual DFT reactivity indices such as the
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Fukui functions, which are related to the local density of states, and the dual descriptor.
These indices should provide us with a picture of the reactivity of the surfaces for
processes where charge transfer is dominant.
Figure 1: Adsorption energy (left) and corresponding Bader charges (right) of a single transition
metal (group 8-11) interacting with an amorphous, hydrated silica slab.
References 1 F. Tielens, C. Gervais, J.F. Lambert, F. Mauri, D. Costa, Chem. Mater., 20, 3336 (2008).
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Bulk band inversion and surface Dirac cones in LaSb and LaBi :
Prediction of a new topological heterostructure
Urmimala Dey1, Monodeep Chakraborty1, A. Taraphder1,2,3 and Sumanta Tewari4
Corresponding author's e-mail address : [email protected] and
phone number : +9199325238961Centre for Theoretical Studies, Indian Institute of Technology Kharagpur, Kharagpur
721302, India2Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
3School of Basic Sciences, Indian Institute of Technology Mandi, HP 175005, India4Department of Physics and Astronomy, Clemson University, Clemson, South Carolina
29634, USAKeywords: Electronic structure, density functional theory, topology, heterostructure.
Abstract
We perform ab initio investigations of the bulk and surface band structures of LaSb
and LaBi and resolve the existing disagreements about the topological property of
LaSb, considering LaBi as a reference. We examine the bulk band structure for band
inversion, along with the stability of surface Dirac cones (if any) to time-reversal-
preserving perturbations, as a strong diagnostic test for determining the topological
character of LaSb, LaBi and LaSb-LaBi multilayer. A detailed ab initio investigation of
a multilayer consisting of alternating unit cells of LaSb and LaBi shows the presence
of band inversion in the bulk and a massless Dirac cone on the (001) surface, which
remains stable under the influence of time-reversal-preserving perturbations, thus
confirming the topologically non-trivial nature of the multilayer in which the electronic
properties can be tailored as per requirement. A detailed Z2 invariant calculation is
performed to arrive at a holistic conclusion.
Reference
1Urmimala Dey, Monodeep Chakraborty, A. Taraphder, Sumanta Tewari, Scientific Reports 8, 14867 (2018).
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Ab initio study of vacancy effect on Mg2X (X=Si, Ge, Sn, Pb)
thermoelectric properties
K. DINE 1*
, A. Dahani 1*
, M. Djermouni 1 and A. Zaoui
1
1LPCM- Computational Physics of Materials Laboratory - University of Sidi Bel Abbes - Algeria
*Faculty of Technology - University of Saida – Algeria
Keywords: thermoelectric, band gap, figure of Merit, Seebeck, power factor
Abstract
in this study , we investigate the effect of vacancy on the thermoelectric properties of four
compounds Mg2X ( X= Si, Ge, Sn, Pb), which are promising thermoelectric compounds
because of their attractive qualities as low cost, chemical stability and environmental
friendliness . we calculate the variation of thermoelectric parameters as figure of Merit ZT,
Seebeck coefficient and Power factor when introducing vacancies. these calculations are
performed in the frame of Density Functional theory, using the Full Potential Linearized
augmented Plane Waves method (FP-LAPW) as implemented in the Wien2k code. To
improve the band gap value, which is an important parameter for the thermoelectric
properties, we use the Generalized Gradient approximation combined with the TB-mBJ
(Tran-Blaha modified Becke-Johnson approach). the results of structural, electronic and
thermoelectric properties are compared with available works.
References
1Tao Fan et al,, RSC Adv,, 8, 17168 (2018).
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First-principles Calculations of the Al-Sc Alloy
Dziri Fatima 1, Belbacha EL-Djemai
2
The aim of the present work, based on ab-initio calculations, is to investigate the relative stabilities of
the different compounds involved in the (Al-Sc) system. Having our calculations performed at 0K,
We will be mainly focusing on the determination of the ground state line of this system.
Our calculations were based on density functional theory (DFT) as implanted in the Vasp code
[1] .We used the projector augmented-wave(PAW) method , which is an all-electrons technique
within the frozen core approximation .Only generalized-gradient approximation(GGA) was
considered. A study of convergence has been done for the plane-wave cutoff energy and allowed us to
fix the Ecut at 360eV. The formation enthalpies of the compounds were obtained through the
following equation: Hf (Alp Scq) = Etot (Alp Scq)- (
E
FCC_A1
EHCP_A3 ,
Where Hf (Bp Znq) is the enthalpy of formation of the compound Alp Scq , Etot(Alp Scq),
E FCC_A1
(Al) and E
HCP_A3 (Sc) are the ground state total energies (per atom) of the compound
Alp Sc q and its constituents Al and Sc, respectively, in FCC_A1
and HCP_A3
structure.
References
[1] : G. Kresse and J. Furthmuller, Efficiency of Ab-Initio Total Energy Calculations for Metals and
Semiconductors Using a Plane-Wave Basis Set, Comput. Mater. Sci., 1996, 6, p 15-50.
Mots clés: Al-Sc Alloy, First-principles
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Probing Structural Changes in the Properties of Matter Using
Extreme Conditions
Emma Ehrenreich-Petersena, Francesca Menescardib, Davide Ceresolib, Justin Jeanneaua, Mads Fonager Hansena, & Martin Bremholma
a Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
b Center for Materials Crystallography and Institute of Molecular Science and Technology
(CNR-ISTM), via Golgi 19, 20133 Milano, Italy
Corresponding author: [email protected], +45 28 15 93 24
Keywords: High pressure, powder X-ray diffraction, evolutionary algorithm, density functional theory, structure solution.
Abstract
There is an increasing interest in the investigation of materials with novel structures
and properties. Synthesis at extreme conditions (high pressures and high
temperatures) is a powerful method to discover new materials, and powder X-ray
diffraction is the key diagnostic tool to investigate structural phase transitions. The
measurements can be conducted in situ under extreme conditions using diamond anvil
cells in which pressures can be increased to >100 GPa while temperatures of
thousands of Kelvin can be achieved by laser-heating. However, these extreme
conditions are detrimental for the data quality and structure solution from experiments
alone is often impossible. Therefore, in this project we use theoretical crystal structure
predictions based on the evolutionary algorithm USPEX1, and subsequent theoretical
calculations to guide the structure solution of compounds at high pressures. The
methodology is illustrated by two projects. Marcasite CrSb2 is a narrow-gap
semiconductor2, that during compression undergoes a phase transition around 12 GPa
to a yet unknown phase. The second project concerns novel nitrogen-rich materials,
where the group of pernitrides is known to have an ultrahigh bulk modulus, e.g. IrN2
with K0 = 428(12) GPa3. Here, we discuss novel nitrides with rare-earth metals that
have been realized experimentally at high pressures and high temperatures.
References
1C.W. Glass, A.R. Oganov, N. Hansen, Computer Physics Communications 175, 713 (2006) 2B.C. Sales, A.F. May, M.A. McGuire, M.B. Stone, D.J. Singh, D. Mandrus, Physical Review B 86, 235136 (2012) 3A.F. Young, C. Sanloup, E. Gregoryanz, S. Scandolo, R.J. Hemley, H.K. Mao, Physical Review Letters 96, 155501 (2006)
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Structural examination of La2SrDyCu2Oy complexities using experimental and theoretical techniques
M.E. Emetere a,b, and Fayomi O.O. a
[email protected], +2348035267598 a Covenant University Canaan Land, P.M.B 1023, Ota, Nigeria
b Department of Mechanical Engineering Science, University of Johannesburg, South Africa
Keywords: Cuprates, High temperature superconductor, Lattice, LSDCO, Structural modulation
Abstract The structural complexities in lanthanum cuprates family were revisited with the aim of understanding factors that structurally triggers long-range repulsive Coulomb interactions [1]. In this study, polycrystalline samples of La2SrDyCu2Oy (LSDCO) were prepared via solid-state synthesis using high purity chemicals [2]. The X-ray diffraction experiment revealed an unusual structural anomaly in the [2 0 5] and [2 1 3] planes of the crystal lattice (Figure 1).
Figure 1: XRD patterns of La2xSrxDyxCu2xOy
The lattice system was further probed using the Niggli-reduced cell at gamma = 6.0678 (Table 1). It was observed that grain boundaries leading to electron trapping originates from the CuO2 plane while the mesoscopic phase separation is controlled by the cell type and axial value in the x- and y-axes of the crystal lattice.
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Table 1: Transformation to a Niggli-reduced cell (gamma = 6.0678)
Atom Cell x Y z Atom O1 2(i) 10.3122 100.801 100.801 O6 O2 2(i) 0.01500 0.01500 0.03000 O1 Cu1 2(i) 0.08400 0.58400 0.16800 Cu1 O3 2(i) 0.09130 0.09130 0.18260 O5 O4 2(i) 0.09500 0.09500 0.19000 O3 Dy 2(i) 0.19500 0.19500 0.39000 Dy1 O5 2(i) 0.20000 0.20000 0.40000 O2 Cu2 2(i) 0.20500 0.20500 0.41000 Cu2 La1 2(i) 0.20870 0.20870 0.41740 La2 O6 2(i) 0.32170 0.32170 0.64340 O1 La2 2(i) 0.58400 0.08400 0.16800 La1 Sr 1(e) 0.60000 0.60000 0.20000 Sr1
Although the research partly supports popular findings that the main positive lobes of LSDCO are centered on the z-axis, it observed that the negative lobe is located in a ring-like structure along the X-Y plane. This result is particularly interesting because it shows the likely origin of broken symmetry in LSDCO sample (Figure 2).
Figure 2: The analyzed SEM image of the LSDCO sample showing different energy levels and grain boundaries
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Investigating the structural modifications in LaAlYbCuO using experimental and theoretical techniques
M.E. Emetere a,b, and Fayomi O.O. a
[email protected], +2348035267598 a Covenant University Canaan Land, P.M.B 1023, Ota, Nigeria
b Department of Mechanical Engineering Science, University of Johannesburg, South Africa
Keywords: Cuprates, High temperature superconductor, Lattice, LSDCO, Structural
modulation
Abstract In this research, we seek a new superconducting candidate LaAlYbCuO based on the need to improve upon the lanthanum cuprates framework [1]. LaAlYbCuO high temperature superconductor was prepared by standard solid-state reaction [1-2]. The characterization was done by the X-ray powder diffraction technique, Scanning Electron Microscopy (SEM) and Rutherford Backscattering Spectrometry (RBS). The analysis of the images was done using Match, Vesta, SRIM, CERN-Root, OMDAQ and Gwydion software. The XRD refinements show that LAYbCO has orthorhombic structure with unit cell as a = 3.865 Å, b = 3.865 Å, c = 19.887 Å (Figure 1).
Fig. 1. XRD patterns of LaAlYbCuO
The specimen had theta correction of 0.19891°. The ratio of electron to phonon production in LAYbCO is approximately 999:1. However, this does not rule-out the possibility of electron-phonon interaction (Figure 2).
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Fig. 2. The target phonon information within LAYbCO sample.
The elemental composition of LAYbCO is given as La1.35Al3.97 Yb6.80Cu6.80O15 at Q-factor – 0.033, Chi-square – 0.6057 and dMax – 173 (Figure 3).
Fig. 3. RBS spectrum.
The new LAYbCO framework showed high chemical homogeneity (Figure 4).
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Structural ,elastic and machanical proprieties of equiatomic
aluminurs compounds
Al-TM (TM=Cu,Fe,Co) from first Principles Calculations.
A.Ferroudj*, Y.Djaballah & Dj.Belbacha
Laboratoire d’Etudes Physico-Chimique des Matériaux (L.E.P.C.M)
Batna 1 University ,Algeria
Keywords: binary aluminium compounds, elastic properties,first principles.
Abstract :
We calculated structural properties, enthalpies of formation of Aluminium –
transition metal binary alloys Al-TM (TM=Cu, Fe,Co) using first principles
calculations based on density functional theory (DFT) within generalized gradient
approximation (GGA) pseudo-potentials and plane waves basis VASP (Vienna ab
initio Software Package). Elastic proprieties has been computed and showed that
these compounds have the strongest alloying ability and structural stability.
A much better agreement was achieved between the Mechanical properties calculated
results and the reported experimental data.
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Barium−Nitrogen Phases Under Pressure: Emergence of Structural
Diversity and Nitrogen-Rich Compounds
Bowen Huang†,‡, Gilles Frapper‡ † Yuelushan, Changsha 410082, PR China
‡ 4 rue Michel Brunet TSA 51106 - 86073 Poitiers Cedex 9, France. [email protected]
(+33) 05 49 45 35 74 † College of Materials Science and Engineering, Hunan University
‡ IC2MP UMR 7285, Université de Poitiers - CNRS
Keywords: Crystal Structure Prediction, DFT, Nitride, High Pressure, High-energy density material, Electride
Abstract
Although the potential of polynitrogen as a high-energy density material (HEDM) has
attracted attention, the difficulty of preserving polynitrogen thwarts attempts to
discover molecular and extended nitrogen structures. Mixing nitrogen with
electropositive elements to obtain viable solid-state compounds represents one
approach to overcome thermodynamic/kinetic instability. In pursuit of barium nitrides
within the Ba−N family, we theoretically explored the ground/meta-stable structures
from ambient pressure up to 100 GPa1. Crystal structure prediction based on
evolutionary algorithms2 and density functional theory identified 13 stoichiometries
and 24 stable structures; several metastable phases were dynamically stable.
Pressure and barium/nitrogen ratio represent controllable factors for polynitrogen net
preparation. Four types of phases could be classified based on nitrogen structural
dimensionality: isolated nitrogen atom; nitrogen molecules, e.g. N2 dumbbells, linear
N3 azides, N4 zigzag units, N5 pentazolate, N6 six-membered rings; 1D polythiazyl
S2N2-like nitrogen chains; and 2D polymeric nitrogen layers. Interestingly, P63/mcm-
Ba3N, R-3m-Ba2N, and C2/m-Ba3N2 have predicted electride properties. Notably, we
observe electronic property changes in the charge-balanced Ba3N2 compound as
pressure increases. Solid-state Ba3N2 changes from a conducting electride at
ambient pressure with encapsulated anionic N2 dumbbells and isolated N atoms to a
nitride semiconductor above 5 GPa in which isolated N3- ions are trapped within a
Ba2+ ocean–as expected for text-book charge-balanced structures–and is metallic
above 25 GPa (Figure. 1). In addition, ab initio molecular dynamics analysis indicate
nitrogen-rich BaN2, BaN4, and bis-pentazolate Ba(N5)2 are quenchable to ambient
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pressure, suggesting these polymeric nitrogen networks can be preserved up to at
least 600 K; these quenchable phases are promising candidate HEDMs.
Figure 1. Predicted Ba3N2 structures at different pressure with space group C2/m
(left), P-1 (middle), C2/c (right).
References
1 B. Huang and G. Frapper, Chem. Mater. 30, 7623 (2018). 2 A.R. Oganov and C.W. Glass, J. Chem. Phys. 124, 244704 (2006).
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Tin-nitrogen binary phase diagram under pressure (0-200 GPa):
emergence of novel SnxNy compositions and polynitrogen nets
Rabii Larhlimi, Busheng Wang, Gilles Frapper [email protected], +33(0)5 49 45 35 74
Applied Quantum Chemistry group, E4, IC2MP, UMR 7285 Poitiers university-CNRS, 4 rue Michel Brunet TSA 51106 - 86073 Poitiers Cedex 9, France.
Keywords: high energy density material, phase diagram, nitride, pressure, polynitrogen nets
Abstract
Although the potential of high pressure polynitrogen phase as a high energy density
material (HEDM) has attracted attention, the difficulty of preserving polynitrogen
towards attempts to discover molecular and extended nitrogen structures. In this field
of crystal structure prediction (CSP), we recently investigated binary phase diagrams
under pressure, ie Mg-N1, Ba-N2. New stoichiometries and stable structures were
identified using crystal structure prediction code (USPEX)3 based on evolutionary
algorithms combined to DFT calculations (VASP)4. Here, we explore binary phase
diagram for tin-nitrogen system from ambient pressure up to 200 GPa and, up to now,
we identified 10 compositions (Sn2N, Sn3N2, SnN, Sn3N4, SnN2, SnN3, SnN4, SnN5,
SnN6 and SnN8). The pressure-composition phase diagram of Sn-N is displayed in
Figure 1.
Figure 1. Pressure-composition phase diagram of Sn-N (PBE GGA PAW).
Pressure - composition phase diagram
Metastable Phases
Stable Phases
Thermodynamical Stability Range
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We studied 21 phases and found 14 dynamically stable phases (10 thermodynamically
stable and 4 thermodynamically metastable). Quenchability of these phases were
studied to check their dynamical stability at ambient pressure.
Several polynitrogen nets are observed in ambient and high pressure Sn-N phases,
eg N2 dumbbells, six-membered N6 rings, finite N8 units, infinite polynitrogen chains,
etc. (See Figure 2). Their electronic and geometrical structures are investigated and
will be presented.
1 2 3
Figure 2. 1, P4/mcm SnN4 at 20 GPa (N2 dumbbells); 2, P-1 SnN4 at 150 GPa
(finite N8 units); 3, P-1 SnN8 at 50 GPa (infinite armchair chains).
Our research is supported by Région Nouvelle Aquitaine FEDER (R.L. PhD fellowship) and PRCI ANR-NSFC Predict_2D_Nanomat (B.W. post-doc support). The calculations were performed at the supercomputers GENCI (Grant n° A0060807539) and Mésocentre SPIN of Poitiers U.
References
1. S. Yu, B. Huang, Q. Zeng, A.R. Oganov, L. Zhang, and G. Frapper, The Journal of Physical Chemistry C 121, 11037 (2017).
2. B. Huang and G. Frapper, Chemistry of Materials 30, 7623 (2018). 3. A.R. Oganov and C.W. Glass, 40 (n.d.). A.R. Oganov, Y. Ma, A.O. Lyakhov, M. Valle, and C. Gatti, in High-Pressure Crystallography, edited by
E. Boldyreva and P. Dera (Springer Netherlands, Dordrecht, 2010), pp. 293–323. A.R. Oganov, A.O. Lyakhov, and M. Valle, Acc. Chem. Res. 44, 227 (2011). C.W. Glass, A.R. Oganov, and N. Hansen, Computer Physics Communications 175, 713 (2006). 4. G. Kresse and J. Furthmüller, Computational Materials Science 6, 15 (1996).
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Predicted two-dimensional silicon nitrides: SiN2, Si3N4, and SiN
Heng ZHANG1,2, Junjie WANG1, Frédéric GUEGAN1, Artem R. OGANOV2,3, Gilles FRAPPER1*
*Email address: [email protected] +33(0)5 49 45 35 74 1Applied Quantum Chemistry group, E4, IC2MP, UMR 7285 Poitiers university-CNRS, 4 rue
Michel Brunet TSA 51106 - 86073 Poitiers Cedex 9, France. 2International Center for Materials Discovery, School of Materials Science and Engineering, Northwestern Polytechnical University, 127 West Youyi Road, Beilin District, Xi'an, Shaanxi
710072, People's Republic of China. 3Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, 3 Nobel St.,
Moscow 143026, Russia.
Keywords: two-dimensional material; nitride; silicon; evolutionary crystal structure prediction; Density functional theory.
Abstract
Ab initio evolutionary algorithm USPEX1-3 is employed for systematic variable-
composition structure prediction of 2D silicon-nitrogen phases. Structures and
energies are computed at PBE GGA PAW and HSE06 levels of theory using VASP
code4-5. Our work unveils a new class of N-rich 2D SixNy compounds, namely SiN2 1,
Si3N4 2, and SiN 3. Their structures are displayed in Figure 1.
1 2 3
Figure 1. Top and side views of 2D SiN2 1, Si3N4 2, and SiN 3 structures.
2D SiN2 1 has a thickness of 1.30 Å and contains N2 dimers coordinated to four
tetrahedral silicon centers. N-N and Si-N single bonds are observed at 1.47 Å and
1.75 Å, respectively (1.49 Å in gas phase N2H4 and 1.74 Å in bulk Si3N4). 1 is an
insulator as expected for this closed-shell structure.
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2D Si3N4 2 possesses an unusual trigonal bipyramid Si3(3-N)2 unit connected to six
planar 3-coordinated nitrogen centers, leading to a Si3(3-N)2N6/3 slab with a
calculated thickness of 2.42 Å. In Si3(3-N)2 cluster, Si-Si distances are 2.38 Å (2.37
Å in bulk silicon), while Si-N bond lengths are 1.83 Å. This original bonding mode is
expected for a 22 valence electron closo Si3N2 cluster (4n+2 rule with n=5). Si3N4 2 is
an insulator (HSE06 gap of 4.8 eV).
SiN 3 is isostructural to isovalent GaS layer found in experimental bulk layered GaS,
with Si-Si and Si-N separations of 2.43 Å and 1.76 Å, respectively. Four-coordinated
silicon and three-coordinated nitrogen atoms follow the octet rule, therefore 3 is
expected to have an open band gap, as computed (2.7 eV at HSE06).
All of the calculated formation enthalpies are negative, at both PBE and HSE06
levels of theory. Moreover, their mechanical, dynamical and thermal stabilities are
demonstrated through investigation of elastic properties, phonon dispersion and ab
initio molecular dynamics simulations.
Others two-dimensional crystalline silicon nitrides will be reported in due course.
Our research was supported by PHC Cai Yuanpei 2019 (Heng ZHANG, CSC fellowship) and PRCI
ANR-NSFC Predict_2D_Nanomat. The calculations were performed at the supercomputers GENCI
(CINES/TGCC, Grant n° A0060807539) and Mésocentre SPIN of Poitiers University.
References
1A. R. Oganov and C. W. Glass, J Chem. Phys. 124, 244704 (2006). 2A. R. Oganov, A. O. Lyakhov, and M. Valle, Acc. Chem. Res. 44, 227-237 (2011). 3A. O. Lyakhov, A. R. Oganov, H. T. Stokes, and Q. Zhu, Comp. Phys. Commun. 184, 1172-1182 (2013). 4G. Kresse and J. Furthmüller, Comput. Mater. Sci. 6, 15-50 (1996). 5G. Kresse and J. Furthmüller, Phys. Rev. B 54, 11169 (1996).
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Effect of absorbing layer thickness on the n-graphene/perovskite/p-
perovskite solar cell
Gagandeep1, a), Mukhtiyar Singh2, Ramesh Kumar1, b) and Vinamrita Singh3
a)[email protected] b) Corresponding author: [email protected]
1Department of Physics, Guru Jambheshwar University of Science & Technology, Hisar, India
2Department of Applied Physics, Delhi Technological University, Delhi, India 3Department of Applied Sciences and Humanities, Ambedkar Institute of Advanced
Communication Technologies & Research, Delhi, India. Key Words: Perovskite, Graphene, Solar Cell, Efficiency, AFORS-HET
Abstract
In the present paper, we simulated the structure of perovskite solar cell
(PSC) as ITO/n-graphene/CH3NH3PbI3/p-CH3NH3PbI3/Ag in AFORS-
HET (Automate for Simulation of Heterostructures) software. To
enhance the performance of PSC, we used the graphene as electron
transporting material due to its high carrier mobility. The p-CH3NH3PbI3
acts as hole transporting materials. In this simulating structure, we
observed the influence of absorbing layer thickness on the performance
parameters of PSC such as Jsc varies from 7.93 mA/cm2
to18.13mA/cm2, Voc varies from 669.5 mV to 688.3mV, FF change from
85.92% to 82.04% and efficiency variation observed from 4.56% to
10.24%. The thickness of absorbing layer is varying from 200-1000 nm.
The J-V graph is obtained under the illumination condition of AM 1.5 G.
The highest efficiency 10.24% is obtained for the optimized thickness of
absorbing layer. We also studied the effect of temperature on the
performance parameters of the solar cells. The spectral response of
simulated structure with wavelength is observed.
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Fig. 1 (a) j-v characteristics of perovskite solar cell (b)variation of solar cell parameter with temperature.
References 1. R.Stangl, J.Haschke and C.Leendertz, Solar Energy, 432, (2009). 2. S.M.Iftiquar, Jung Soo Kim and Junsin Yi, Optik.148, 54-62, (2017). 3. Kamlesh Patel and PawanK.Tyagi. Carbon, 116, 744-752, (2017).
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Luminescent LnIII-based Complexes with Phenanthroline
for Smart Optical Materials: A Theoretical Study
Tsvetan Zaharieva, Boris Borrissova,b, Ivelina Georgievaa, Natasha Trendafilovaa, Nina Danchovab, Stoyan Gutzovb
aInstitute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, "Acad. Georgi Bonchev" str., bld.11, Bulgaria
bFaculty of Chemistry and Pharmacy, Sofia University ‘St. Kliment Ohridski’, 1164 Sofia, 1 James Bourchier Blvd., Bulgaria
aCorresponding author: [email protected]; +359 2 979 2592 bCorresponding author: [email protected]; +359 2 8161 281
Keywords: lanthanide complexes, antenna-chromophores, intersystem crossing, energy transfer, TD-DFT, Semiempirical methods
Abstract
Lanthanide-based compounds are highly valued for their photoluminescent properties. Their line-like emission results in high colour purity of the emitted light and it is characterized by a sharp, well-defined spectral interval. Such properties are extremely valuable for the development of smart optical materials for lighting, telecommunications, displays, lasers, security inks, molecular thermometers, sensors, bioimaging and immunoassays1. An established strategy to stimulate the luminescence of LnIII-ions is the complexation with antenna-chromophores2. When irradiated with UV-light, the sensitized complexes undergo a complex sequence of relaxation processes, which includes intersystem crossing between singlet and triplet excited states and ligand-to-metal energy transfer3. A more detailed knowledge on the distinctive steps of the sensitization mechanism can contribute to the design of highly luminescent LnIII-based complexes. In particular, quantum chemistry methods can be employed to determine the correlation between molecular and electronic structure of the complexes, on the one hand, and observed quantum yields, and lifetimes, on the other. Sensitization in Ln(NO3)3(Phen)2 and Ln(C4H8NCS2)3Phen (Ln ≡ EuIII,TbIII; Phen ≡ 1,10-phenathroline) are studied with the help of TD-DFT and Semiempirical methods. Energy diagrams, S1 and T1 excited state character and the concurrent energy transitions. CASSCF method including perturbative spin-orbit coupling estimates, is employed to assess the rates of intersystem crossing between the lowest singlet excited states and the respective triplet excited states of the complexes. Ligand-to-metal energy transfer mechanisms and the emission properties of the lanthanide ions were modelled with the help of semi-empirical Sparkle/RM1 and INDO/S-CIS methods, as well as, Judd-Ofelt theory, and the QDC model of Freire and co-workers. All theoretical estimates are validated by comparison with available experimental results. The factors that stimulate the high emission intensities and contribute to the efficiency of light conversion are discussed.
Acknowledgements: The financial support by the Bulgarian Science Fund, Grant DH09/ 9/2016 is greatly acknowledged. Part of the calculations was performed at the computer cluster of the Bulgarian Academy of Sciences “MADARA”. We also
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acknowledge the provided access to the e-infrastructure of the NCDSC – part of the Bulgarian National Roadmap on RIs, with the financial support by the Grant No D01-221/03.12.2018. References
1 J.C.G. Bunzli, European Jounal of Inorganic Chemistry, 5058-5063 (2017).
2 J.C.G. Bunzli, Coordination Chemistry Reviews 293, 19 (2015).
3 P.A. Tanner, L. Zhou, C. Duan, K.-L. Wong, Chemical Society Reviews 47, 5234 (2018).
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Phase transition dependence of elastic constants and related
parameters for rocksalt-CsCl MgO structures
S.Djaili , Faculty of Science,Amar telidji University of Laghouat, Laghouat, Algeria
00213550306647
A.Gueddim , Faculty of Science and Technology,Ziane Achour University of Djelfa, , Djelfa, Algeria
00213550595861.
Keywords:MgO,abinitio calculation, elastic constants.
Abstract
The aim of this work was the study of high-pressure behavior of MgO periclase's
elastic constants using abinitio total energy calculations within the full-potential
linearized augmented plane. We used the wave method in the framework of the
density functional theory. We predict that at 612GPa pressure MgO rocksalt
structure transit to CsCl structures so the elastic constants such as the bulk modulus,
shear modulus, Young’s modulus, anisotropy factor, Poisson’s ratio were changed,
also these parameters were calculated in different pressure conditions
References
1A. Gueddim, N. Bouarissa,, A. Villesuzanne, Optik 124 (2013) Energy levels and deformation
potentials for rocksalt MgO 2A. Gueddim, N. Bouarissa, A. Villesuzanne, Computational Materials Science 48 (2010) Pressure
dependence of elastic constants and related parameters for rocksalt MgO 3Y. Fei, Am. Mineral. 84 (1999), Effects of temperature and composition on the bulk modulus of
(Mg,Fe)O, 4John E. Jaffe, James A. Snyder, Zijing Lin, Anthony C. Hess, PHYSICAL REVIEW B 62 ( 2000), LDA
and GGA calculations for high-pressure phase transitions in ZnO and MgO
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The effect of H-bonding interactions on conformational changes in functionalized imidazolium ionic liquid : Experimental vibrational
spectroscopy (ATR-IR and Raman) and DFT Evidence.
Boumediene Haddad a,b,c, Johannes Kiefer d , Annalisa Paolonee,, Didier Villemin c, Sumit Kumar Panja f, Drai Mokhtar b, Mostafa Boumediene a , Serge Bresson g,
Mustapha Rahmouni b.
a Department of Chemistry, Dr Moulay Tahar University of Saida , Algeria. b Synthesis and Catalysis Laboratory LSCT, Tiaret Univ Tiaret, Algeria
c LCMT, ENSICAEN, UMR 6507 CNRS, University of Caen, 6 bd Ml Juin, 14050 Caen, France.
d t Bremen, Badgasteiner Str. 1, 28359 Bremen, Germany.
e CNR-ISC, U.O.S. La Sapienza, Piazzale A. Moro 5, 00185 Roma, Italy fDepartment of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore
560012, Karnataka, India. g Laboratoire de Physique des Systèmes Complexes, Université Picardie Jules Verne, 33 rue
St Leu 80039 Amiens cedex, France. Auteur correspondant : E-mail ; [email protected]
Phone number: +213667223956
Keywords: Ionic liquid; H-bonding Interaction; IR and Raman analysis; Ion pair; Cluster formation; Density Functional Theory (DFT)
Abstract
The chemical and physical properties of ionic liquids are determined by the
interactions between the cation-anion couples. Hence, unravelling the relationships
between the microscopic and the macroscopic scales is the key for a rational design.
In the present work, we make a step towards understanding how the effect of H-
bonding interactions on conformational changes in functionalized imidazolium ionic
liquid as an example.
For this purpose, vibrational spectroscopy (ATR-IR and Raman) and quantum
chemical theory (DFT) were employed to investigate the H-bonding assisted cluster
formation and inter molecular interactions in functionalized imidazolium IL.
Preferential strong alkyl CH2−OH···Cl interaction wasobserved between the
mostacidic hydrogen atom of hydroxyl alkyl group of imidazole cation ring and Cl
anion where the anion is located at the top ofimidazole cation ring with the help of
experimental and theoretical studies. The C2−H···ClH-bonding interaction is observed
and assist to form dimeric ion-pair cluster. Further, it is also observed that methyl and
alkyl groups does not interact with the Cl anion. The presence of intermolecular
interactions and cluster formation were discussed with results of experimental and
theoretical observations.
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Our work shows that further contribution methods theoretical techniques and
experimental effort is necessary to finally unravel the structure-property relationships
of this fascinating class of materials.
. References
1S.K. Panja, B. Haddad, J. Kiefer, ChemPhysChem, 19 (22) (2018), pp. 3061-3068
2S.K. Panja, B. Haddad, M. Debdab, J. Kiefer, Y. Chaker, S. B Bresson, A. Paolone,
ChemPhysChem (2019)
https://doi.org/10.1002/cphc.201801206 3B. Haddad, A. Paolone, D. Villemin, J.F. Lohier, M. Drai, S. Bresson, E.H. Belarbi, J. Mol. Liq., 260
(2018), pp. 391-402 4B. Haddad, A. Paolone, M. Drai, M. Boumediene, D. Villemin, E.H. Belarbi, O. Abbas, J. Mol.
Struct., 1175 (2019), pp. 175-184
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First principle modelling of the point defects migration at the
InN/GaN and InGaN/GaN interfaces
R. Hrytsak 1,2 , P. Kempisty 1 , E. Grzanka 1,3 , J. Smalc-Koziorowska 1,3 , A. Lachowski 1 , S. Grzanka 1,3 , M. Leszczynski 1,3 , and M. Sznajder 2
1 Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland
2 Faculty of Mathematics and Natural Sciences, University of Rzeszow, Pigonia 1, 35-959 Rzeszow, Poland
3 TOPGaN LTD. Sokolowska 29/37, 01-142 Warsaw, Poland email: [email protected]
Keywords: ab initio calculations, nitrides, point defects, diffusion.
Abstract
The nitride semiconductors GaN, InN, and AlN and their alloys are very attractive for
a wide application in optoelectronics. Light emitting diodes (LEDs) and laser diodes
(LDs) utilize InGaN/GaN quantum wells as active materials grown by MOVPE or
MBE methods. Efficiency of the light emitting diode is still a big technological issue,
especially in the green region of spectrum. Point defects can drastically affect the
optical properties of the devices, especially diffusion of point defects can lead even to
the decomposition of quantum wells at high temperatures during the p-type layers
growth.
Our first principle calculations are performed in the framework of the density
functional theory (DFT) by means of Siesta program1. The electron exchange-
correlation effects are treated within the generalized gradient approximation (GGA)
using the Perdew-Burke-Ernzerhof (PBEJsJrHEG) form of the exchange-correlation
functional. The electron ion-core interactions are represented by the Troullier-Martins
type pseudopotentials and the electron wave-functions are expanded into the atomic-
orbital basis set using the triple-ζ polarized set. The semi-core cation d states of
Ga(3d) and In (4d) are treated as local valence orbitals. The cutoff of 500 Ry is used
for the real space mesh. During the structural optimization procedure of atomic
positions in the bulk crystals atom's coordinates are allowed to change until the
largest force component is less than 0.01 eV/Å. Using the optimized lattice constants
of bulk GaN and InN crystals, a supercell containing 384 atoms with an orthorhombic
shape is constructed, which represents InN/GaN or InGaN/GaN heterostructures.
This supercell is employed in calculations of the energy barriers encountered at the
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migration of neutral and charged point defects VN, VGa, VIn, VAl. In particular, we model
six types of interfaces In1-xGaxN/GaN (x=0.75, x=0.25, x=0), where the Inx-1GaxN
material is strained to GaN, or the In1-xGaxN/GaN heterostructure is fully relaxed. We
consider defect migration in the growth direction of heterostructure (c-direction), as
well as in lateral directions. The results of modelling enable tracing of the preferred
directions for migration and accumulation of vacancies.
The obtained so far results show that (i) in the case of In0.25Ga0.75N/GaN strained with
respect to GaN, charged VN3+ diffuse with smaller energy barrier than the neutral
ones, (ii) it is possible for VN3+ to accumulate near the In0.25Ga0.75N/GaN interface, in
the In0.25Ga0.75N material, (iii) neutral VGa vacancies can be created easier in the bulk
part of In0.25Ga0.75N and GaN materials than at the In0.25Ga0.75N/GaN interface, (iv) the
diffusion of neutral VGa both from the bulk GaN material and from the bulk In0.25Ga0.75N
material towards the In0.25Ga0.75N/GaN interface proceeds with decreasing energy
barrier. Hence, an accumulation of neutral VGa vacancies can be observed near the
In0.25Ga0.75N/GaN interface.
Our results are in a good agreement with experimental data concerning the
decomposition of InGaN/GaN quantum wells.
Acknowledgements: The authors thank the TEAM/2016-3/26 project that is carried
out within the TEAM programme of the Foundation for Polish Science co-financed by
the European Union under the European Regional Development Fund.
References
1J. Soler, E. Artacho, J. D. Gale, A. Garcia, J. Junquera, P. Ordej on, D. Sanchez-Portal, The SIESTA
method for ab initio order-N materials simulation, J. Phys.: Condensed Matter 14, 2745 (2002).
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A first-principles study of the structural and transport properties of
stannoidite compounds.
A. Huguenot1, B. Fontaine, X. Rocquefelte1, J.-F. Halet1, P. Lemoine1, S. Cordier1, E. Guilmeau2, R. Al Rahal Al Orabi3, R. Gautier1
1 Institut des Sciences Chimiques de Rennes UMR 6226, Avenue du Général Leclerc, CS
50837, 35708 Rennes Cedex 7, France [email protected], 0223236537
[email protected], 0223238122 2 Laboratoire de Cristallographie et Science des Matériaux, UMR 6508 CNRS/ENSICAEN, 6
boulevard du Maréchal Juin – CS 45053 – 14050 Caen Cedex 4 3 Solvay, Design and Development of Functional Materials Department, Axel'One, 87 avenue
des Frères Perret, 69192 Saint Fons, Cedex, France
Abstract
The demand in energy consumption has been escalating this past decade, leading to
renewed interest in thermoelectric (TE) technology. Beyond the promising results
obtained for telluride based materials which exhibit high performances[1], the need to
conciliate efficiency with environmental and cost constraints have triggered research
recently toward copper-based sulfides which have, for the most part, the advantage
to contain eco-friendly and abundant elements.
Two classes of copper-based sulfides can be distinguished, exhibiting n-type and p-
type conductivities, respectively. The n-type class is obtained for lower copper
content materials. The p-type class of copper-based sulfides covers a broad range of
compositions, from Cu/M ratio equal or close to 1, as exemplified by the stannites
Cu2ZnXS4 (X = Sn and Ge)[2] to copper-rich sulfides, with Cu/M ratios ranging from 2
to 5 as shown by Cu2SnS3[3] and the derivatives of tetrahedrite Cu12Sb4S13
[4] colusite
Cu26V2Sn6S32[5] and bornite Cu5FeS4
[6].
Recently, a univalent copper hyper-stoichiometric stannoidite Cu8+xFe3−xSn2S12[7] with
0 ≤ x ≤ 0.5 has been synthesized using mechanical alloying followed by spark plasma
sintering. The transport properties show a remarkable crossover from a
semiconducting to a metal-like behavior as the copper content increases from x = 0
to x = 0.5, whereas correlatively the Seebeck coefficient decreases moderately, with
S values ranging from 310 to 100 μV/K. The thermal conductivity decreases as the
temperature increases showing low values at high temperature, far below those
reported in related stannite materials. The investigation of the thermoelectric
properties shows that the ZT figure of merit is dramatically enhanced by the copper
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hyper-stoichiometry by a factor of 5 going from 0.07 for x = 0 to 0.35 for x = 0.5 at
630 K.
In order to better understand these transport properties, a density functional theory
study of stoichiometric and hyper-stoichiometric stannoidite have been carried out.
Since Cu and Fe atoms occupy similar crystallographic sites, special attention has
been paid to the structural properties of these compounds and compared with X-ray
diffraction and 57Fe and 119Sn Mössbauer experiments. The thermoelectric properties
are analyzed via calculations based on the Boltzmann transport equation under a
constant relaxation time approximation.
References
1 J. R. Sootsman, D. Y. Chung, M. G. Kanatzidis, Thermoelectric Materials. Angew. Chem., Int. Ed. 48, 8616−8639 (2009).
2 (a) M. L. Liu, F. Q. Huang, L. D. Chen, I. W. Chen, Appl. Phys. Lett.94, 202103 (2009), (b) C. P. Heinrich, T. W. Day, W. G. Zeier, G. J. Snyder, W. Tremel, J. Am. Chem. Soc.136, 442−448 (2014).
3 Y. Shen, C. Li, R. Huang, R. Tian, Y. Ye, L. Pan, K. Koumoto, R. Zhang, C. Wan, Y. Wang, Sci. Rep. 6, 32501 (2016).
4 (a) K. Suekuni, K. Tsuruta, T. Ariga, M. Koyano, Appl. Phys. Express 5, 51201 (2012), (b) X. Lu, D. T. Morelli, Y. Xia, F. Zhou, V. Ozolins, H. Chi, X. Zhou, C. Uher, Adv. Energy Mater. 3, 342−348 (2013), (c) T. Barbier, P. Lemoine, S. Gascoin, O. I. Lebedev, A. Kaltzoglou, P. Vaqueiro, A. V. Powell, R. I. Smith, E. Guilmeau, J. Alloys Compd. 634, 253−262 (2015).
5 (a) K. Suekuni, F. S. Kim, H. Nishiate, M. Ohta, H. I. Tanaka, T. Takabatake, Appl. Phys. Lett. 105, 132107 (2014), (b) C. Bourges, M. Gilmas, P. Lemoine, N. Mordvinova, O. I. Lebedev, E. Hug, V. M. Nassif, B. Malaman, R. Daou, E. Guilmeau, J. Mater. Chem. C 4, 7455-7463 (2016), (c) Y. Kikuchi, Y. Bouyrie, M. Ohta, K. Suekuni, M. Aihara, T. Takabatake, J. Mater. Chem. A 4, 15207−15214 (2016).
6 (a) P. Qiu, T. Zhang, Y. Qiu, X. Shi, L. Chen, Energy Environ. Sci. 7, 4000 (2014), (b) G. Guelou, A. V. Powell, P. Vaqueiro, J. Mater. Chem. C 3, 10624−10629 (2015), (c) V. P. Kumar, T. Barbier, P. Lemoine, B. Raveau, V. Nassif, E. Guilmeau, Dalt. Trans. 46, 2174 (2017).
7 V. Pavan Kumar, T. Barbier, V. Caignaert , B. Raveau, R. Daou, B. Malaman, G. Le Caër, P. Lemoine, E. Guilmeau, J. Phys. Chem. C, 121 (30), 16454–16461 (2017).
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Topology of Hg-based chalcogenides – ab intio studies
Rajibul Islam1,Wojciech Brzezicki
1, Timo Hyart
1, Carmine Autieri
1 and Tomasz Dietl
1,2
[email protected] (+48-796759656), [email protected] l,
[email protected], [email protected] ,
1 International Centre for Interfacing Magnetism and Superconductivity with Topological
Matter – MagTop, Institute of Physics, Polish Academy of Science, Warsaw, Poland
2 WPI-Advanced Institute for Materials Research Tohoku University, Sendai, Japan
Abstract
The research on topological materials emerges as one of the most active fields in the condensed
matter physics. We have investigated the electronic topological properties of the bulk and
interface of Hg-based chalcogenide materials (HgX, X=S, Se, Te) by means of the density
functional theory. To have a better insight on the topological properties of the interface, we have
studied the electronic band structure at the interface between these materials and the trivial
insulator CdTe. The Weyl semimetal phase is found for such interfaces. Furthermore, we have
examined the interface between different Hg-based chalcogenides. Finally, we have investigated
the effect of strain demonstrating significant changes of the topological properties.
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First Principle Study of a Push-Pull Type Small Organic Molecule
with Ambipolar Characteristics and Rich Linear and Non-Linear
Optical Properties
Dwaipayan Chakraborty and Priya Johari
Email: [email protected], Ph. No: +91 9920101349
Department of Physics, School of Natural Sciences, Shiv Nadar Univesity, NH91, Tehsil Dadri, Greater Noida, Uttar Pradesh- 201314, India
Shiv Nadar Univesity, Greater Noida, India
Keywords: Organic semiconductor, Small molecule, Push-pull structure, Mobility, Non-linear Optics
Abstract
Organic Semiconductor (OS) is an emerging class of energy materials, for its several
advantages over its inorganic counterpart, such as large area, flexibility, low cost and
most importantly their environment friendly manufacturing process1. Computational
designing and study of new semiconducting organic molecules has come up as a
great support in this regard. Push-pull type small organic molecule has recently
gained a huge scientific research owing to their remarkable charge transfer
properties, high non-linear optical response, reduced HOMO-LUMO gap and hence
broad range of absorption spectrum, air stability etc. which collectively promotes this
class of molecules as potential candidate for non-linear optical devices, OFETs and
organic solar cells2. In this effort, we therefore rationally designed a promising
Donor(D)-π-Acceptor(A) (i.e, push-pull) type molecule NNDM-NH2, a trans-stilbene
derivative. We predicted its crystal structure starting from the experimental crystal
structure of another stilbene derivative and calculated the charge transport
properties, electronic band structure, gas phase linear and non-linear optical
properties. We also did the Hirshfeld surface analysis and plotted the molecular
electrostatic potential to get insight into the structure-property correlation. We found
that this new organic semiconductor owns a high charge carrier mobility of ~ 2.11
cm2/Vs for hole and 0.64 cm2/Vs for electron, together with desirable electronic and
linear and non-linear optical properties revealing NNDM-NH2 as a potential candidate
for the opto-electronic devices.
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References
1Yuning Li, Prashant Sonar, Leanne Murphya and Wei Honga, Energy & Environmental Science 6, 1684 (2013).
2Filip Bure, RSC Advances 4, 58826 (2014)
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Structural and vibrational properties of boron nitride
Michal Novotný*, Luigi Cigarini*, František Karlický*
*Department of Physics, Faculty of Science, University of Ostrava,30. dubna 22, 701 03 Ostrava, Czech Republic
[email protected]+420 553 46 2155
Keywords: hexagonal boron nitride, phonon spectra, stacking, DFT, dispersion correction
Abstract
Hexagonal boron nitride (h-BN) is an interesting material proposed as a candidate for
new generation of solar cells, chemical sensors and a wide range of very promising
applications. Although it has been thoroughly experimentally and theoretically studied
some of its most basic structural properties still remain unknown. In our work we
provide a deeper insight and accurate calculation on the stability of different stacking
orders in bulk hexagonal boron nitride at the density functional theory (DFT) level of
electronic structure theory. We provide an overview on the accuracy of all the
different dispersion correction methods available in the VASP code when calculating
the lattice constants, cohesion energies and bulk moduli as well as provide a
comparison between the various approaches and algorithms employed in their
calculation. From this we have selected the best method to calculate lateral sliding
briers as well as phonon spectra of the various stacking orders by a finite
displacements approach.
References
1 A. Shmeliov, J. S. Kim, K. B. Borisenko et al., Nanoscale 5, 2290 (2013)2 Kresse G and Hafner J, Phys. Rev. B 48, 13115 (1993)3 Giannozzi, Paolo, et al., J. Phys. Cond. Matt. 21, 395502 (2009)4 Liu, Lei, Y. P. Feng, and Z. X. Shen, Phys. Rev. B 68, 104102 (2003)
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Ab Initio Study of Structural, electronic and thermal Properties of U3Si2
under pressure
M. KHALFA1, S. HADJI1, S. KORICHI2, H. BOUCHERIT1, H. KHACHAI3
1 Centre de Recherche Nucléaire de Draria, BP 43 Sebala, Draria, Algiers, Algeria
2Commissariat à l’Energie Atomique (COMENA), BP 399 Alger gare, Algiers, Algeria
3Applied Materials Laboratory (AML), Physics Department, Djillali Liabes University of Sidi Bel-Abbes, Algeria
Email address : [email protected]
Mobile: 00213661805094
Keywords: Silicide compounds, Nuclear fuel, FP-LAPW, structural properties, thermal
properties
Abstract
Binary uranium-silicon compounds have been extensively investigated for years due
to its potential to be used in the next generation nuclear fuels. There are several
compounds in the binary uranium-silicon system such as U3Si, U3Si2, U5Si4, USi,
USi3, USi2, USi1.88 and U3Si5 U3Si2 and U3Si have seen most extensive study as
dispersion plate type fuel for research reactors due to their higher uranium density.
Compare to U3Si, the U3Si2 compound is found to be more suitable for its
implementation as LEU (LEU, below 20 wt% U235) fuel because of several reasons
such as stability against growth of fission gas bubbles, low swelling, better
compatibility with aluminium etc.., U3Si2 has been licensed as a dispersion type fuel
in an aluminum matrix by the Reduced Enrichment for Research and Test Reactors
(RERTR) Program since 1988 1,2,3, and qualified by the U.S. Nuclear Regulatory
Commission and released for sale with uranium densities up to 4.8 gU/cm3. 4
A theoretical study of structural, electronic and thermodynamic properties of U3Si2,
were studied by means of the full-relativistic version of the full-potential augmented
plane wave plus local orbital's 5. We employed both within the generalized-gradient
approximation (GGA) 6 for exchange and correlation. The relativistic corrections to
the total energy have been accounted by incorporating the spin-orbit interactions in
the total energy calculations. The GGA+U method is used to explore the effect of
orbital dependent potentials, which are applied to the 5f states in uranium 7,8 to
capture their correlated nature. The implementation of GGA+U applied here is
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rotationally invariant, meaning that an “effective” Ueff = (U – J) is used, where J is set
to zero.
At room temperature, U3Si2 stabilizes into tetragonal structure with space group
P4/mbm reported by Zachariasen 9 and later examined by Dwight 10. We note that
GGA+SO appear more accurate and stable than GGA+Ueff, with Ueff=1, 1.1, 1.2, 1.3,
1.5, 2 et 3, well as metal-rich compounds are often not well described by high U
values and the preferred choice is typically to use GGA without any Hubbard U
parameter (Ueff = 0.0 eV) 11. The GGA+SO without any Hubbard are used in all
calculations in this study.
The ground state properties, lattice and bulk modulus constants with GGA+SO are
agree well with available experimental and theoretical data, in electronic properties
we seen that the DOS of U3Si2 and U spectrum with SO coupling is more delocalized
compare to that without SO coupling and 5f orbital of U and 3p orbital of Si is mainly
participating in the bonding of U3Si2. Many thermo-physical properties of solids, such
as specific heat, thermal expansion, Debye temperature, Entropy are study in this
work, in the temperature range from 0 to 1900 K which is below the melting point of
U3Si2 (1938 K) and the pressure from 0 to 50 GPa. It is seen that the saturation value
of heat capacities of U3Si2 is ~123 J/mol.K above 600 K This is the Dulong-Petit
classical limit.
References
1A. Travelli, The U.S. reduced enrichment for research and test reactor program, in: Proc. (1978) Int. Mtg. on RERTR, Argonne, IL, (1978). 2Safety Evaluation Report Related to the Evaluation of Low-enriched Uranium-Silicide Dispersion Fuel for Use in Non-power Reactors, July (1988). Report of the US Nuclear Regulatory Commission, Report NUREG-1313. 31999 International Meeting on Reduced Enrichment for Research and Test Reactors, Budapest, Hungary, October 3-8, (1999). 4U.S.Regulatory Commission. Safety Evaluation Report related to the Evaluation of Low-Enriched Uranium Silicide-Aluminum Dispersion Fuel for Use in Non-Power Reactors. Jul (1988). 5Madsen G K H, Blaha P, Schwarz K, Sjostedt E and Nordstrom Phys. Rev. B 64 195134 (2001). 6Perdew J P, Burke S and Ernzerhof M Phys. Rev. Lett.77 3865 (1996). 7V. I. Anisimov, I. V. Solovyev, M. A. Korotin, M. T. Czyzyk, and G. A. Sawatzky, Physical Review B 48, 16929 (1993). 8A. I. Liechtenstein, V. I. Anisimov, and J. Zaanen, Physical Review B 52, R5467 (1995). 9W.H. Zachariasen, Acta Crystallogr. 2 94-99 (1949). 10A.E. Dwight, ANL-82e14, Argonne National Laboratory, Argonne, 1L, (1982). 11Noordhoek, M. J., Besmann, T. M., Andersson, D., Middleburgh, S. C., & Chernatynskiy, A.. Phase equilibria in the U-Si system from first-principles calculations. Journal of Nuclear Materials, 479, 216-223 (2016).
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Possible p-type doping with a Sodium atom: a theoretical study
Said Kheira ,Baghdede Rachide.
C2MO, Engineering Physics Laboratory (LGP), Matter Sciences Faculty, Ibn
Khaldoun University,14000, Tiaret, Algeria
213. 05.61.10.77.97
Ibn Khaldoun University
Keywords: Wurtzite- ZnO, DFT Theory , Castep code, Band Structure, Loss Function .
Abstract
The present work is a theoretical study of a most element Na that attracted much interest of
the research community for p-type realisation effect on electronic and optical properties of
zinc oxide (ZnO) wurtzite structure, using the density functional theory (DFT) which is
developed to calculate the electronic states of solids containing huge numbers of electrons1.
The band structure and Density of States (DOS) diagrams are plotted from the optimized
equilibrium lattice parameters, an effective of Na approach is describe to modify the
electronic properties of ZnO with a 55 electrons near the Fermi level, moreover we could
observed a high loss energy along the range (10nm-50nm) the strong peaks near 270nm for
ZnO and ~830nm for ZnO Na are mainly caused by the bulk phonon excitation in very low
energy near 120nm may be due to multiple inter-band transitions2, while other ZnO doping
locate at the low energy region.
Additionally, the presence of impurity of Na significantly decrease the transmittance of ZnO
which is expected to provide new applications of industrial optoelectronic and
photovoltaic.Our calculations provide reasonable interpretation for the experimental findings.
References
1Takao Tsuneda,
1Density Functional Theory in Quantum Chemistry 978-4-431-54824-9, Springer
Japan 2014.
2Yang Sun; Huan Xu; Bo Da; Shi-feng Mao; Zen-jun Ding, CHINESE JOURNAL OF CHEMICAL
PHYSICS(2016).
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Accurate many-body calculation of electronic and optical band gap
of bulk hexagonal boron nitride
Miroslav Kolos1; František Karlický1
1Univ Ostrava, Fac Sci, Dept Phys, 30 Dubna 22, CZ-70103 Ostrava, Czech Republic
AbstractMany-body perturbational GW approximation in conjunction with the Bethe-Salpeter
equation (BSE) has been employed to calculate accurate electronic and optical band
gaps of bulk hexagonal boron nitride (h-BN) in the two most important stacking
configurations, AA and AB. The carefully converged results revealed h-BN as an
indirect material (indirect gap approximate to 6.1 eV) with a huge excitonic effect
(approximate to 0.8 eV) in perfect agreement with recent experiments [Nat.
Photonics, 2016, 10, 262; Appl. Phys. Lett., 2016, 109, 122101]. The K-H region of
the first Brillouin zone has been shown as the most important for lowest optical
excitations in h-BN. Surprisingly, simple scissor corrected DFT has described h-BN
band structure at the GW level and subsequent time-dependent DFT with a suitable
exchange correlation kernel has provided absorption spectra similar to the full
GW+BSE spectra.
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Investigation of structural, elastic, mechanic and
thermodynamic propreties of transition metal iodid
perovskites (M=Hf, Pt and Pd) .
*H.Krarcha1,2 & B.Bennacer1
*email: [email protected]
1 Physics Laboratory at Guelma, Faculty of Mathematics, Computing and Material
Sciences , University 8 Mai 1945 Guelma, P.O. Box 401 Guelma 24000, Algeria 2 Primalab laboratory, Department of physics, Faculty of material sciences,University
Batna1, Batna 0500, Algeria
Keyword: first principles, perovskites , elastic properties.
Abstract:
First-principles pseudo-potential linearized augmented plane-wave method
based on density functional theory is used to investigate the structural, elastic
and thermodynamic properties of the cubic iodid perovskites
Cs2MI6 (M=Hf, Pd and Pt) within the local density approximation (LDA) and
generalized gradient approximation (GGA) for potential exchange correlation.
Basic physical mechanic properties related to elastic constants (Cij) such as
shear modulus G, Young’s modulus, E, poisson ratio , and Anisotropy factor
A. The calculated energy band structures show that the cubic perovskite
Cs2MI6 are semiconductor.
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Theoretical investigation of pressure induced topological phase
transition in TmSb
Payal Wadhwa1, Shailesh Kumar2(a),(b), Alok Shukla3, Rakesh Kumar1*
1Department of Physics, Indian Institute of Technology Ropar, Rupnagar – 140001, Punjab,
India
2(a)School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland 4000, Australia
2(b)Manufacturing Flagship, CSIRO, Lindfield West, New South Wales 2070, Australia
3Department of Physics, Indian Institute of Technology Bombay, Powai – 400076, Mumbai, India
*e-mail: [email protected]
*Contact No. - +911881242164
e-mail of presenting author: [email protected]
Keywords: Topological insulators, Topological semi-metals, Density functional theory
Abstract
Recently, extremely large magnetoresistance (XMR) materials like WTe2, Bi2Te3, etc.
have attracted greater attention to study exotic topological properties. Further, XMR
effect has been found to be greatly pronounced in rare-earth monopnictide
compounds LnX, (where Ln is a rare-earth element and X = As, Sb, Bi); amongst
which some are topologically trivial for example, LaSb, YSb, etc. [1] and others are
non-trivial for example, LaBi, CeBi, etc. [2]. Till now, XMR effects are explained on
the basis of electron-hole compensation [3] and topological protection [4], where the
role of electron-hole compensation is well understood by two-band model, while the
role of topology is yet to be established. It motivated us to investigate a topologically
trivial XMR material, in which non-trivial topological phase can be induced by
increasing the strength of spin-orbit coupling, which may be used as a test material to
understand the relation between topology and XMR effect. In this work, we report the
emergence of topological phase in XMR material TmSb as a function of hydrostatic
pressure using first principles calculations. At ambient pressure, TmSb is found to be
topologically trivial, but undergoes a topological phase transition at a hydrostatic
pressure of ~12 GPa and becomes topologically non-trivial. With further increase in
pressure, it again becomes topologically trivial at ~15 GPa, which is far below the
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pressure of its structural phase transition. Therefore, the findings would help
experimentalists to explore a correlation between topology and XMR effect.
References
1R. Lou et al, Phys. Rev. B 95, 115140, (2017).
2L.-K. Zeng et al, Phys. Rev. Lett. 117, 127204 (2016).
3M.-N. Ali et al, Nature 514, 205 (2014).
4J Jiang et al, Phys. Rev. Lett. 115, 166601 (2015).
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Electronic and vibrational properties of Copper Indium Selenium: a first-
principles study
Sandeep Kumar and Ludger Wirtz
Physics and Materials Science Research Unit, University of Luxembourg, 1511 Luxembourg, Luxembourg
Email: [email protected]
Phone: +352661976654 Keywords: CuInSe2, Density functional Theory, Lattice Dynamics, DFPT
Abstract
We have performed first-principles calculations of the electronic structure and the lattice
dynamics of CuInSe2 both in the chalcopyrite structure and with Cu-Au ordering of the cation
sublattice. We have used density functional theory (DFT), as implemented in the Vienna Ab
initio Simulation Package (VASP). Since the semi-local PBE and LDA functionals lead to a
closure of the gap for both phases of CuInSe2, we investigate – via the use of the HSE06 hybrid
functional - the effect of Hartree-Fock exchange on the band-structure and the resulting phonon
frequencies. The calculated Raman and infrared active phonon frequencies are in reasonable
agreement with the experimental values and other calculations.
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DFT study of novel 3D C60 polymers
J. Laranjeiraa, L. Marquesa, N. Fortunatoa, M. Melle-Francob, K. Strutyńskib and M. Barrosoc. ([email protected] 00351 914 410 266)
a Departamento de Física and CICECO, Universidade de Aveiro, 3810 Aveiro, Portugal. b Departamento de Química and CICECO, Universidade de Aveiro, 3810 Aveiro, Portugal.
c Departamento de Física and I3N, Universidade de Aveiro, 3810 Aveiro, Portugal.
Keywords: DFT, high pressure high temperature, polymerized C60, electronic structure, x-ray diffraction.
Abstract
New three-dimensional (3D) C60 polymerized structures, in which each molecule
adopts either one of the two standard orientations, have been investigated using the
density functional theory (DFT) method. Ordered binary-alloy type structures (AuCuI,
Au3Cu, CuPt, “A2B2”) were used as prototypes in constructing 3D C60 polymerized
structures, one standard orientation corresponding to the A atom and the other
orientation to the B atom. DFT structural optimizations show that intermolecular
bonds, 56/56 2+2 cycloaddition, form between molecules with different orientations
but no intermolecular covalent bond is formed between similarly oriented molecules,
and, thus, the intermolecular covalent bonding can be mapped on to the
antiferromagnetic interaction. This intermolecular bonding type forms between two
intramolecular single bonds of neighbouring molecules and differs from the more
common 66/66 2+2 cycloaddition that forms between intramolecular double bonds.
The electronic and elastic properties of these polymerized structures were also
calculated, within the general gradient approximation framework, at room pressure
and at 9.5 GPa. All these structures show metallic behaviour [1] and their bulk moduli
range from 88 to 132 GPa [2]. These 3D polymerized structures are likely to be
prepared at 9.5 GPa and 550ºC, although the observed fcc structure points to a
disordered/frustrated structure, which is characteristic of the Ising antiferromagnetic
interactions in the fcc lattice [3].
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Figure 1 crystal structure, electronic band structure and density of states of the
AuCuI-type C60 polymer structure
References
1J. Laranjeira, L. Marques, N. Fortunato, M. Melle-Franco, K. Strutyński, M. Barroso, Carbon 137, 511-518 (2018). 2J. Laranjeira, L. Marques, M. Melle-Franco, K. Strutyński (to be published). 3J. Laranjeira, L. Marques, M. Mezouar, M. Melle-Franco, K. Strutyński, Phys. Stat. Sol. RRL 11, 1700343 (2017). Ackowledgment: This work was developed within the scope of the project POCI-01-0145-FEDER-031326 financed by FCT and co-financed by FEDER and project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES.
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First-principles calculation of phonon: Raman scattering in Nb2Se9
nanowire
Junho Lee1, Bumjun Kim2, Jae-young Choi2,3* and Joonsuk Huh1,3*
1Department of Chemistry, Sungkyunkwan University, Suwon 16419, Republic of Korea 2School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon
16419, Republic of Korea 3SKKU Advance Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon
16419, Republic of Korea
* E-mail: [email protected] and [email protected]
* Phone number: +82-10-2730-4050 and +82-10-6644-5330
Keywords: transition metal chalcogenide, nanowire, one dimensional material, density-functional perturbation theory, Raman scattering
Abstract
The one-dimensional transition metal chalcogenide material niobium-selenide
(Nb2Se9) nanowires was successfully synthesized in recent years. We present
experimental Raman scattering on Nb2Se9 and theoretically calculated Raman
spectrum using the density functional theory (DFT) for the first time. 22 well-resolved
Raman modes were observed, 13 modes in low wavenumber range (50 ~ 200 cm-1)
and 9 modes in high wavenumber range (220 ~ 340 cm-1). The unit cell consists of
two Nb2Se9 formula units (Z = 2) and all atoms are in (2i) symmetry position of P1
space group. The 33 Ag modes are predicted to be Raman active from group analysis.
Raman Spectra is calculated within both local-density approximation (LDA) and
generalized gradient approximation (GGA). In low wavenumber range, LDA
functional predict peak position well while GGA functional predict better in high
energy range of Raman spectrum. We expect that these results will provide a
platform of the after research, characterization of single strand and bulk in Nb2Se9
nanowire thorough Raman scattering.
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Laser Induced Desorption, The Future of Diamond Nanostructuring?
Keri Liang1, Catherine Stampfl1, Leigh Weston1,2, and Rich Mildren2
1School of Physics, The University of Sydney, Camperdown NSW 2006;
[email protected] (02 9351 2636), [email protected]
(61 2 9351 5901), [email protected] (61 2 935 17726)
2MQ Photonics Research Centre, Department of Physics and Astronomy, Macquarie University,
New South Wales 2109, Australia; [email protected] (61 2 9850 8965)
Abstract
Interest in diamond technology has been gaining momentum in recent decades. The
unique properties of diamond, such as its high transparency, semiconducting properties,
chemical inertness, and biocompatibility, has found it numerous applications in
electronics, resonant optical cavities, waveguides, and medicine. As desirable are
diamond’s potential applications, it is these properties of diamond that make them
notoriously difficult to process, especially on the nanoscale. Traditionally, processing of
diamond surfaces has involved mechanical polishing, laser ablation, plasma etching, and
ion implantation. These methods although effective, are incapable of achieving the high
fidelity as seen in other semiconductors1. Thus, there is need for processing techniques
of higher precision for the manipulation of diamonds.
A new and promising technique involving a two-photon laser induced desorption
mechanism (LID) has recently been reported which could solve many of these problems2.
The process involves irradiating oxygen passivated surfaces of diamonds with photons
of energies close to the band gap, resulting in carbon monoxide molecules being ejected,
taking along with them carbon atoms of the surface. This happens even if the laser fluence
is well below that required for ablation. This threshold-free process is truly an atomic scale
surface manipulation, with etch rates as low as 3×10-9 nm/pulse achievable for low
incident fluence1, 2, 3. Although, a number of distinguishing features of LID have been
discovered over the years, its exact mechanism is still unclear. In order to gain
understanding into the mechanism responsible for the ejection, we perform first-principles
(density functional theory) calculations using the VASP code. We initially investigate the
adsorption of oxygen, for a wide range of coverages, on low-index diamond surfaces (see,
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e.g. Figure 1(a) for selected structures on the (100) surface). From these results we
identify and predict the stable/metastable structures. For the identified oxygen surface
structures, we then investigate the interaction of UV laser pulses on the diamond surfaces
using first principles time-dependent density functional theory calculations2. The results
for the (100) surface showed that the carbon ejection mechanism involves direct laser-
induced excitation of the surface carbonyl groups, into a triply bonded carbon-monoxide
like state. While at the same time, breaking the underlying carbon-carbon bonds (Figure
1(b)). Investigations will also be performed for the other low-index surfaces as well as
stepped surfaces to obtain a more complete picture of the phenomenon.
Figure 1: (a) Top view (I), and side
view (II) of different oxygen (red)
adsorption sites on hydrogen (blue)
terminated diamond (yellow) surfaces.
(b) Diamond surface carbonyl group,
before (I) and after (II) a laser pulse.2
References
1MS Komlenok, VV Kononenko, VG Ralchenko, SM Pimenov, and VI Konov. Laser induced nanoablation
of diamond materials. Physics Procedia, 12:37–45, 2011.
2Weston, L., et al. "Photochemical Etching of Carbonyl Groups from a Carbon Matrix: The (001) Diamond
Surface." Physical Review Letters 122.1 (2019): 016802.
3CG Baldwin, JE Downes, CJ McMahon, C Bradac, and RP Mildren. Nanostructuring and oxidation of
diamond by two-photon ultraviolet surface excitation: An XPS and NEXAFS study. Physical Review B,
89(19):195422, 2014.
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Influence of addition elements-induced anisotropy and defects on the
mechanical behavior of the transition metal aluminide alloys : ab initio
investigation
Souheyr Meziane e-mail address: [email protected], [email protected], +213(0)558018281, Tlemcen
13000 -AlgeriaUnité de Recherche Matériaux et Energies Renouvelables – URMER, Université de Tlemcen,
AlgeriaEcole Supérieure en Sciences Appliquées, B.P. 230, 13000 Tlemcen, Algeria
Keywords: Intermetallics; Mechanical properties; TM-Al; Ab initio; VASP code.
Abstract
Intermetallics have attracted significant research interest due to their unique combination
of stiffness, low density, creep and high temperature strength as primary properties,
optimized and acceptable levels of ductility, toughness, fatigue resistance and
environmental resistance required for many technological applications [1]. In the general
case, the main property sought is the improvement of the ductility of these materials at
ambient temperature Up to now, titanium aluminides have been used for the GenxTM 1B
(Boeing 787) and the GenxTM 2B (Boeing 747-8), and nickel aluminide alloys have
attracted interest for turbine engine applications [2]. However, their use remains very
limited because of the lack of ductility. Indeed, in TiAl alloys, the addition of Nb together
with low aluminum content usually induce the formation of micro- segregation in the matrix,
which is harmful to the room-temperature ductility and high-temperature creep resistance
[3]. The main goal of this study is to optimize the mechanical properties of intrinsic ductility
at ambient temperature.
In this study, density functional theory and ultra-soft pseudo-potential method implemented
in the VASP (Vienna Ab initio Simulation Package) code, with generalized gradient
approximation (GGA) are used to investigate the structural, mechanical and electronic
properties for the transition metal aluminides TM-Al. The comparison of calculated
equilibrium lattice parameters, bulk modulus, chemical bonding from the density of states
and experimental data shows very good agreement.
References :
[1] Bushra Fatima, Sankar P. Sanyal, Computational Condensed Matter 14, 144–152 (2018). [2] Yao Jiang, Yuehui He, C.T. Liu, Intermetallics 93 (2017). [3] Ruirun Chen, Qi Wang, Yaohua Yang, Jingjie Guo, Yanqing Su, Hongsheng Ding, Hengzhi Fu,Intermetallics 93, 47–54 (2018).
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Formation of suspended Fluorine magnetic layers in intercalated
graphene
Shashi Bhusan Mishra1, Satyesh kumar Yadav
2, and B. R. K. Nanda
1
1Condensed Matter Theory and Computational Lab, Department of physics, IIT Madras, Chennai, India. 2Department of Metallurgical and Materials Engineering, IIT Madras, Chennai, India.
Email- Id: [email protected]
Abstract
Functionalization of graphene plays a major role in a wide range of technological applications,
especially in the area of electronics, catalysis, mechanics and energy storage. Particularly
inducing long range magnetic ordering through functionalization in graphene and its composites
is one of the hotly pursued research subjects in the area of mesoscopic physics. Through density
functional calculations, transition state theory and molecular dynamics simulation here we
propose that a suspended pseudo-atomized fluorine layer can be stabilized between two sets of
mono/multilayer graphene. More importantly each of the pseudo-atomized fluorine generates
local spins without perturbing the graphene band structure. These spins align with the neighbors
ferromagnetically with a coupling strength close to 70 meV. Therefore, the fluorine intercalated
graphene/graphitic layers hold great promise for futuristic spintronics applications.
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Proton Dynamics in Organic Ferroelectrics using First
Principles MD Simulations and Neutron Scattering
Sanghamitra Mukhopadhyay, Matthias Gutmann and Felix Fernandez-Alonso
Rutherford Appleton Laboratory, Science and Technology Facilities Council, UK Research and Innovation, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX
[email protected] +441235778190
Keywords: Organic ferroelectric, proton dynamics, density functional theory, molecular dynamics, neutron scattering
Abstract
Hydrogen bonded organic ferroelectrics are important functional materials for potential technological applications in flexible electronics as low power high speed ferroelectric memories, in energy storage devices as super capacitors, and in medical ultrasound devices as ferroelectric capacitors1. Croconic acid (C5O5H2) (CA) is one of that kind of material. At the molecular level CA is a pentagonal monocyclic oxoacid where intramolecular-delocalization favors the acidic tautomer, characterized by the presence of two vicinal hydroxyl groups within the same molecular unit. In solid CA the pentagonal rings of individual CA molecules are arranged in hydrogen-bonded layers and pleated sheets reminiscent of an accordion.
Crystalline CA is reported as a single component above-room-temperature organic ferroelectric2. Prior to this work, ferroelectricity in organic materials had been restricted to polymers or multi-component molecular solids relying on charge or proton transfer across chemically distinct donor-acceptor pairs3. These exciting developments encouraged to investigate the structure, dynamics and the mechanism of high temperature ferroelectricity including the role of hydrogen bonding interactions and hydrogen motions in this seemingly simple organic crystal4-7.
We employed state-of-the-art calculations using CASTEP code and PBE+D functional based on plane wave pseudo potential density functional theory (DFT) to predict the structure, vibrational and polarizability properties of CA at its ground state and compared with in-house neutron diffraction and inelastic neutron spectroscopy (INS) experiments. Our calculations and temperature dependent inelastic neutron scattering experiments (INS) predicted that proton motions in CA was anharmonic and mechanism of ferroelectricity had been explained in the light of Jahn-Taylor type distortion of the hydrogen bonded network4-7 .
We analysed quasi-elastic neutron scattering (QENS) experiments using first principles molecular dynamics (MD) simulations using CASTEP code. Calculations using more than 300 atoms and 0.5fs MD step a production run more than 10ps was performed. The calculations helped to identify two different types of motions of two protons in CA located at terrace and hinge positions. The neutron observables were calculated using MDANSE code and compared with QENS experiments done on IRIS instrument at ISIS. Our calculations predicted a start of rotational motion of protons
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above 200 K and a jump type translational motion above 300K leading to distortion of the crystal structure8. These findings were important to explain the room temperature ferroelectricity in this novel material.
References
1E. Taghaddos, M. Hejazi and A. Safari, J. Adv. Dielectrics 5, 1530002 (2015).
2S. Horiouchi, Y. Tokunaga, G. Giovannetti, S. Picozzi, H. Itoh, R. Shimano, R. Kumai and Y. Tokura, Nature, 463, 789 (2010)..
3A. Stroppa, D. D. Sante, S. Horiuchi, Y. Tokura, D. Vanderbilt, S. Picozzi, Phys. Rev. B, 84, 014101 (2011).
4F. Fernandez-Alonso, M. J.Gutmann, S. Mukhopadhyay, D. Jochym, K. Refson, M. Jura, M. Krzystyniak, M. Jimnez-Ruiz, and A. Wagner, J. Phys. Soc. Jap 82, SA001 (2013).
5S. Mukhopadhyay, M. J. Gutmann, M. Jura, D. B. Jochym, M. Jimenez-Ruiz, S. Sturniolo, K. Refson, and F. Fernandez-Alonso, Chem. Phys, 427, 95 (2013).
6S. Mukhopadhyay, M. J. Gutmann, and F. Fernandez-Alonso, Hydrogen-bond Structure and Anharmonicity in Croconic Acid, Phys. Chem. Chem. Phys., 16, 26234 (2014).
7S Mukhopadhyay, M. J. Gutmann, M. Jimenez-. Ruiz, D. B. Jochym, K. T. Wikfeldt, K. Refson, F. Fernandez-Alonso, Phys Chem Chem Phys 19, 32216, (2017).
8S Mukhopadhyay, M. J. Gutmann, F. Fernandez-Alonso, to be submitted (2019).
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Interaction of the H2 molecule with carbon nanostructures: A DFT
study
Dominik Nöger, David HolecDepartment Materials Science, Montanuniversität Leoben, Roseggerstraße 12, 8700
Leoben, [email protected], +43 3842 402 1813
DFT, VASP, hydrogen, graphene nanotubes, adsorption
Abstract
On a long path of finding appropriate materials to store hydrogen, graphene and
carbon nanotubes have drawn a lot of attention as potential storage materials. Their
advantages lie at hand since those materials provide a large surface area (which can
be used for physisorption), are cheap compared to metal hydrides, are abundant
nearly everywhere, and most importantly, can increase safety to existing storage
solutions. Therefore, a great variety of theoretical studies were employed to study
those materials. After a benchmark study of different van-der-Waals corrections to
Generalized Gradient Approximation (GGA), the present Density Functional Theory
(DFT) study employs Tkatchenko-Schaffler (TS) correction to consider long-ranged
dispersion interaction. The main subject of the study was the influence of point and
line defects in graphene on the physisorption of the hydrogen molecule. For point
defects our research mainly targeted the impact of vacancy and Stone-Wales
defects. Furthermore the adsorption behaviour of a line defect (22.8 degree large
angle grain boundary) in graphene was investigated. Finally, the study presents the
impact of different carbon nanotube diameters and chiralities (zigzag & armchair
confguration) on physisorption energetics and behaviour.
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Structural prediction of a ZrTiO2 mixed oxide. A DFT study
F. Ortiz-Chi1, L. Badal-Torres2, H. N. Fernández-Escamilla3, N. Cob-Calan4, C. G. Espinosa-Gonzalez1, S. Godavarthi1, M. E. Cifuentes-Quintal5, E. Martínez-
Guerra3, and G. Torres-Torres2
Corresponding author e-mail: [email protected]
1CONACyT-Universidad Juarez Autonoma de Tabasco, Centro de Investigación de Ciencia y Tecnología Aplicada de Tabasco, C.P. 86690, Cunduacán, Tabasco, México; 2Universidad Juarez Autonoma de Tabasco, División Académica de Ciencias Básicas, C.P. 86690, Cunduacán, Tabasco, México; 3Universidad Autónoma de Nuevo León, Facultad de Ciencias Físico Matemáticas, San Nicolás de los Garza, N.L., México; 4Instituto Tecnológico de Conkal, División de Estudios de Postgrado e Investigación, C.P. 97345, Conkal, Yucatán, México; 5Departamento de Física Aplicada, Centro de Investigación y de Estudios Avanzados del IPN, C.P. 97310, Mérida, Yucatán, Mexico.
Keywords: Catalysis, Mixed oxides, Structural prediction
Abstract
Although TiO2 is used to get ultraviolet light, its overall solar activity is still very
limited. The search for superior catalytic systems has motivated the development of
novel doped, mixed, and tuned supported clusters. By itself, the prediction and
elucidation of new catalytic supports is one of important challenges in material
modelling; besides being of great technological interest. In this work we propose a
zirconium titanate system as an alternative to already reported systems based on
single and mixed titanium and zirconia dioxides1-3. The reported crystal structure was
found by performing a structural search from scratch with the USPEX code4. For the
proposed structure we calculated the phonon band structure and used phonon
dispersion relations to investigate the structural stability. In addition, we performed a
study of the relative stability of the low-index surfaces. All the structural relaxations
and related electronic structure calculations were performed in the DFT framework as
is implemented in the VASP code5. Our results indicate that the proposed TiZrO4
system is feasible to exist and that their low-index surfaces can be used in later
theoretical works to understand the complex catalytic activity in mixed oxides based
on TiO2. We are grateful to CONACyT (Grant A1-S-26876) by financial support and
the HPC Juchiman (CONACyT, U0003-2015-7-26609) for the allocation of
computational resources.
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References
1V. Polliotto, S. Livraghi, A. Krukowska, M.V. Dozzi, A. Zaleska-Medynska, E. Selli, E. Giamello, ACS Appl. Mater. Interfaces 10, 27745 (2018) 2V. Polliotto, E. Albanese, S. Livraghi, P. Indyka, Z. Sojka, G. Pacchioni, E. Giamello, J. Phys. Chem. C 121, 5487 (2017) 3H. Dutta, A. Nandy, S.K. Pradhan, J. Phys. Chem. Solids 95, 56 (2016) 4A.O. Lyakhov, A.R. Oganov, H.T. Stokes, Q. Zhu, Comput. Phys. Commun. 184, 1172 (2013) 5G. Kresse, J. Furthmuller, Phys. Rev. B 54, 11169 (1996)
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The role of exchange interactions on spin reorientation transition of
Nd0.5Dy0.5FeO3: A first principle study
Sarita Rajput1 , Padmanabhan B1,2, V.K.Malik1, T.Maitra1
1Department of Physics. Indian Institute of Technology Roorkee, Roorkee 247667, India
2Department of Allied Sciences, Graphic Era University, Dehra Dun,248002, India
The rare-earth orthoferrites (RFeO3) which are known for their spin-reorientation and
other interesting properties like magneto-dielectric effect show a large Neel temperature
of 700 K, below which the Fe3+ spins order as G-type antiferromagnet in the
configuration Γ4 (Gx,Ay,Fz). Magnetic properties and electronic structures of rare-earth
orthoferrite Nd0.5Dy0.5FeO3 have been studied by performing accurate first principle
calculation based on density functional theory. Among the various possible magnetic
configurations of Fe3+ spins with the frozen Nd/Dy 4f states, the G-type ordering
emerges as the ground state. Both, NdFeO3 and DyFeO3, order in entirely different
magnetic configurations. From our calculations it is found that C-type magnetic
structure emerges as the lowest energy state of Nd3+/Dy3+, which is well in agreement
with experiments. The spin-reorientation and the ground state of Fe3+ moments are
evaluated using non-collinear calculations with spin-orbit coupling. With inclusion of 4f
states of Nd/Dy, the Γ2 structure emerges as lowest energy in the Fe3+ spins which is
thereby consistent with experiment and symmetry analysis. Estimation of exchange
interactions by mapping the system to Heisenberg model yields a competing Nd-Fe and
Nd-Dy and Dy-Dy exchange interactions in comparison to much smaller Dy-Fe and Nd-
Nd interactions. Hence, it is clear that the Nd3+ -Fe3+ and Nd3+ -Dy3+ exchange
interactions play a dominant role in large polarization of the rare earth ions which
prevent independent ordering of the Nd3+ - Dy3+ moments.
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First principles study of Pt/MgO (100), Pt/MgO/GaAs (110) and
MgO/Pt/GaAs (110) heterojunctions to estimate schottky barrier
hight, band offset and I-V charactristics
M. Ramesh, Manish K Niranjan
Department of Physics, Indian Institute of Technology, Hyderabad, Near NH-65, Sangareddy,
Kandi, Telangana 502285, INDIA.
Abstract
The first principles density functional theory and nonequilibrium greenes function (NEGF) framework
have been used to study the Pt/MgO (100), Pt/MgO/GaAs (110) and MgO/Pt/GaAs (110) interface
properties such as schottky barrier hight (SBH), band offset and I-V charactristics. The calculated band
gaps of MgO and GaAs were mached with experimental value for metta-GGA (mgga) exchage
correlations. We analysed n-SBH of metal-insulator (Pt/MgO) interface for various doping densities (n-
type), biase voltage and exchage correlations. The Pt/MgO interface at zero bias voltage, we found large
n-SBH for mgga than LDA calculations. These results shows, n-SBH value decreases with increasing
n-type doping density. We applied bias voltage +0.5 V for left and right electrode of Pt/MgO supercell,
n-SBH is higher by 0.95 eV and compared with zero voltage. The Pt/MgO/GaAs (110) interface, n-
SBH of Pt/MgO interface is high due to large dipoles at the interface. Further, second interface
(MgO/GaAs) shows band offset. The MgO/Pt/GaAs (110) interface, the n-SBH is small due to the metal
dipoles are shared by both the interfaces. Pt/MgO interface I-V characteristics shows schottky diode
nature with small forward voltage drop. These properties significantly useful in power rectification for
electronic devices.
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Computational Analysis of Au-Pd Nanoalloy: A DFT Study
Prabhat Ranjan Department of Mechatronics Engineering, Manipal University Jaipur, Dehmi Kalan, Jaipur-
303007, INDIA Email- [email protected]
Keywords: Density Functional Theory; HOMO-LUMO Energy Gap; Au-Pd; Hardness;
Abstract
The study of bimetallic nanoalloy clusters is an active field of research due to its
interesting electronic, optical, magnetic and catalytic properties. Among several
bimetallic nanoalloy clusters, the compound formed between Au-Pd is of great
importance due to its catalytic behaviours. Density Functional Theory (DFT) is one of
the most popular approaches of quantum mechanics to study the electronic
properties of matter. Conceptual Density Functional Theory (CDFT) based
descriptors have turned to be an essential tool for investigating and correlating the
experimental properties of compounds. In this report, we have studied the physico-
chemical properties of cationic [AunPd]+ (n=1-6) nano alloy clusters by using Density
Functional Theory methodology. In this report, we have computed the DFT based
descriptors and try to correlate with experimental counter parts. The study reveals
that computed HOMO-LUMO energy gap and molecular Hardness have direct
relationship. The computed HOMO-LUMO energy gap also show odd-even
oscillation behaviour with the number of total atoms present in the cluster. The high
value of correlation coefficient between HOMO-LUMO energy gap and DFT based
descriptors supports our analysis. The computed data are in line with the
experimental data.
References
1W. Kohn, L. J. Sham, Phys. Rev. 140, A1133 (1965). 2H. K. Yuan, A. L. Kuang, C. L. Tian, H. Chen, AIP Adv. 4, 037107 (2014).
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Computational and Experimental Investigation
of the Gold Surface Alkylation Mechanism
Igor Rončević,a Katarina Varga,a Jiří Kaleta,a,b Jyh-Chiang Jiang,c Josef Michla,b
[email protected], +420 220 183 449 aInstitute of Organic Chemistry and Biochemistry of the CAS, Prague, Czech Republic
bDepartment of Chemistry, University of Colorado, Boulder, United States cTaiwan Tech University, Taipei, Taiwan
Keywords: gold alkylation, surface reactions, periodic boundary conditions, DFT, GC-MS spectrometry, vibrational spectroscopy
Abstract
The formation of self-assembled monolayers (SAMs) on metallic surfaces is a very
interesting topic, with many possible applications. 1,2 Recently, the direct alkylation of
gold surface, resulting in the formation of a C-Au bond, has been shown to produce
stable monolayers.3 However, not much attention has been given to the alkylation
mechanism, although an aerogel-based study showed that many side-products are
formed.4
Here, new experimental and computational insights about the mechanism of gold
surface alkylation are presented. SnBu4 was used as a substrate, as the butyl chain
transfers efficiently and it is short enough to be modelled computationally. Experiments
were performed by adding a very small amount of SnBu4, dissolved in chloroform,
between two large gold plates separated by about 0.2 mm. GC-MS of the subsequently
analyzed solution revealed the presence of butene, octane, and SnBu3Cl, suggesting
that elimination, dimerization and solvent-assisted desorption take place. To confirm
these findings, experiments with deuteriated SnBu4 were performed as well.
The alkylation was analyzed computationally using the PBE-D2 method as
implemented in VASP. Minima and transition structures were modelled on a
reconstructed five-layer 111 gold surface. The calculations of adsorption energies at
various packing suggested that the alkyl SAMs achieve similar high coverage as their
thiol counterparts, and the comparison of calculated and experimental IR and Raman
spectra provided further proof for the existence of the C-Au bond. The computed
barriers for elimination and dimerization confirmed that these reactions can indeed take
place at room temperature, while their transition structure geometries showed that they
preferably occur at low or moderate packings, which was experimentally backed by
time-resolved experiments. Finally, a low barrier was calculated for the movement of
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butyl groups across the gold surface, explaining the formation of islands with high
packing.
References
1. L. Newton, T. Slater, N. Clark, A. Vijayaraghavan, J Mater Chem C 1, (3), 376 (2013). 2. J. C. Love, L. A. Estroff, J. K. Kriebel, R. G. Nuzzo, G. M. Whitesides, Chem Rev 105, (4), 1103 (2005) 3. E. Kaletova, A. Kohutova, J. Hajduch, J. Kaleta, Z. Bastl, L. Pospisil, I. Stibor, T. F. Magnera, J. Michl, J Am Chem Soc 137, (37), 12086 (2015) 4. M. Benkovicova, J. Wen, J. Plutnar, M. Cizkova, A. Eychmuller, J. Michl, J Phys Chem Lett 8, (10), 2339 (2017)
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Structural, mechanical, Density of state, bonding feature and
thermodynamic properties of the R-Ag(R= Y, La, Ce, and Dy) and R-Cu
(R=Y, Dy, Ho and Er) rare-earth intermetallic compounds:
First principles investigation analyzed with Data Mining tools.
A.Sekkal 1, 2, F. Saidi2, M. Sahlaoui3, 4, A. Benzair5, C. Esling6 and J.M. Raulot6
Corresponding author. Tel: +213 559 211 627 Email address: [email protected]
1 Ecole Supérieure en Sciences Appliquées d’Alger(ESSA), Algérie 2Division EPM, Unité de Recherche Matériaux et Energies Renouvelables, Université
Abou Bekr Belkaid, B.P 119, 13000 Tlemcen, Algérie. 3 Laboratoire de Physique Théorique, Université de Tlemcen, 13000 Tlemcen, Algérie.
4 Ecole Supérieure en Sciences Appliquées de Tlemcen, BP 165 R.P, 13000 Tlemcen, Algérie.
5Département de physique, Faculté des Sciences, Université Djilali Liabés Sidi Bel Abbés.
6Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux, LEM3 UMR CNRS 7239, Université de Lorraine UL, Metz 57045, France.
Abstract: In this work, The full-potential linearized augmented plane wave (FP-LAPW) method
have been used to examine various properties of YAg, LaAg, CeAg, DyAg, YCu,
DyCu, HoCu and ErCu members of a class of fully ordered stoichiometric
intermetallics with the CsCl-type B2 crystal structure. These compounds have been
found to have significant polycrystalline ductility at room temperature. The calculated
ground state properties such as lattice constants, bulk Modulus and elastic constants
agree well with the available data. The ductility or brittleness of these materials is
predicted. For ErCu and HoCu compounds. The mechanical and Debye temperature
are predicted from the calculated values of elastic constants. The analysis of the
density of states (DOS) gives a detailed explanation of the contribution of atomic
orbital characters in the energy bands. The thermodynamic properties also are
predicted by the quasi-harmonic Debye model in the temperature range 0-700 K. In
addition, chemical bonding of some compounds investigate here has been
investigated in the light of topological analysis approach based on the theory of
atoms in molecules. The relationship between several thermo-physical and
mechanical properties were discussed, and analyzed with data mining techniques.
The obtained results confirm that this B2-type of rare-earth intermetallic compounds
have very interesting mechanical and thermal properties for structural applications.
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Keywords: Intermetallic compounds; Ab-initio calculations; Electronic structure ; Elastic properties ; Thermodynamic and Bonding properties; Theory of Atoms in Molecules (AIM); Data Mining technique.
References
1A.M. Russell, Z. Zhang, K.A. Gschneidner Jr, T.A. Lograsso, A.O. Pecharsky, A.J. Slager, D.C.
Kesse, Intermetallics 13, 565 (2005). 2K. A. Gschneidner, A.Russell, A.Pecharsky, J.Morris, Z.Zhang, T.Lograsso, et al.Nature Mater 2, 587
(2003). 3A.Sekkal, A. Benzair, H. Aourag, H.I. Faraoun, G. Merad. Physica B 405, 2831– 2835 (2010).
4A. Sekkal, A Benzair, T. Ouahrani, H.I. Faraoun, G. Merad, H. Aourag, C. Esling. Intermetallics 45,
65-70 (2014).
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Half Metallic ferromagnetism in Ti-doped BaSe: A first principles
study
Poonam1, [email protected], +919812939197
Hardev Singh2, [email protected], +919728915004
Manish K. Kashyap3 [email protected],+919467210306 1,2Department of Physics, Guru Jambheshwar University of Science & Technology, Hisar-
125001, Haryana (India)
3Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)
Keywords: Spintronic, half metallicity, DFT, FPLAPW
Abstract
The electronics and magnetic properties of Ti-doped BaSe compound at dopant
concentration, x=12.5% have been investigated using full potential linearized
augmented plane wave (FPLAPW) method based on density functional theory (DFT)
as implemented in WIEN2k. The exchange and correlation (XC) effects have been
taken into account by an orbital independent modified Becke–Johnson (mBJ) potential
as coupled with Local Density Approximation (LDA). The dopant Ti modifies
significantly the ground state properties of host BaSe compound. The resultant
compound (Ba0.88Ti0.12Se) shows half metallicity with 100% spin polarization at EF
and can be characterised as true half-mettalic ferromagnet (HMF). The appearance of
half-metallicity in this compound is due to hybridization between Ti-d and Se-p states.
The total magnetic moment is mainly attributed to Ti-d states. Further, very small
magnetic moments induced on other nonmagnetic atoms (Ba and Se) also strengthen
the total moment. The existence of magnetism along with half-metallic gap make the
compound suitable for spintronic applications.
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Enhancing GaSe Catalysis for Hydrogen Evolution Reaction via Ni
Doping and External Electric Field
Ephrem Gizachew Demissie, Wai Kit Tang, Chi-Kit Siu Addressee: Hall 8, Room 903, Student Residence of City University of Hong Kong, 22
Cornwall Street, Kowloon Tong, Hong Kong Email: [email protected]
Phone number: +85263774767 Department of Chemistry, City University of Hong Kong, Kowloon Tong, Hong Kong
Keywords: GaSe, band engineering, electric field, doping, hydrogen evolution reaction
Abstract
Two-dimensional (2D) Gallium selenide has ignited intensive attention for their potential
application of water splitting due to its semiconducting nature [Schaibley et al., 2016].
Unfortunately, pure GaSe has an indirect and wide band gap [Jung et al., 2016]. For more
practical applications, it is highly desired to translate the GaSe into direct and narrow
band-gap semiconductors by controlling external parameters. This study provides a
systematical investigation of the fundamental electronic properties and possibility of
indirect to direct band-gap transition of GaSe through Ni doping and external electric field
based on density functional theory (DFT) using the HSE06 functional. Our results reveal
that although there is no translation between indirect to direct band gap upon Ni doping,
the band gap size has been reduce to the optimum value for water splitting reaction.
However, by applying an external electric field, we observed that the ability to fine tune
the position of valence band of Se states and translate to direct band gap, which can give
an optimal H adsorption strength on GaSe for HER. The present study would open a new
method to control and design of GaSe-based catalysts for future industrial applications.
Refernce
1J.R. Schaibley, H. Yu, G. Clark, P. Rivera, J.S. Ross, K.L. Seyler, W. Yao, X. Xu, Nat. Rev. Mater. 1 16055, (2016) 2C.S. Jung, K. Park, F. Shojaei, J.Y. Oh, H.S. Im, J.A. Lee, D.M. Jang, J. Park, N. Myoung, C.-L. Lee, et al., Chem. Mater. 28 5811, (2016) Chem. Mater. 28 (2016), 5811−5820
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Spin orientation transition across graphene-ferromagnet
interface: first principles study
Kumneger Tadelea;b, Qinfang Zhanga
aSchool of Materials Science and Engineering, Yancheng Institute of Technology, P.O.Box 224051, Yancheng, PR China bApplied Physics, College of Natural Sciences, Adama Science and Technology University, P. O. Box 1888, Adama, Ethiopia
Keywords: graphene, ferromagnet, interfaces, spin-orbit-coupling, first-principles
calculation
The interfacial interaction between graphene and ferromagnetic substrate is
known to bring additional controls to the intrinsic properties of graphene, in
addition to, probably, inducing some novel properties to the system which may
have potential application in spintronics and computing. In this work the spin-
polarized electronic structures across the graphene-ferromagnet interface has
been investigated using first principles density functional theory calculation as it
is implemented on Vienna ab-initio simulation package (VASP). The electronic
and magnetic properties of the interface have also been investigated. In this
study the ferromagnet substrate was represented by Ni(111) and Co(111)
surfaces due to their structural resemblance to graphene. The study reveals that
the ferromagnet layers adjacent to the interface show a transition of spin
orientation from in plane to out of plane. Strong hybridization between different
orbitals of graphene and ferromagnet was observed. The hybridization
significantly affects the electronic and magnetic properties of the interface.
Reduction on the local magnetic moments of the ferromagnet layers adjacent to
the interface and induced spin polarization on the graphene layer are some of the
observed impacts of the hybridization. This work provides important information
which can be used for efficient design of interfaces for graphene-based
spintronics.
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Ab initio Simulations of XAS spectra for Li-ion batteries
Beata Taudul1,2*, Marie-Liesse Doublet1,2
*[email protected] Charles Gerhardt, CNRS UMR5253, Université Montpellier 2, 34 095 Montpellier, France
2Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, France
Keywords: Li-ion batteries, Li-rich transition metal oxides, anionic redox, X-ray absorption
spectroscopy, ab initio calculations
Lithium-ion batteries operate on cationc redox reactions accompanied by insertion-
deinsertion of Li+. They are nowadays primary energy source for portable electronics and
of great importance for electric transportation. To meet increasing market requirements,
improvement of batteries parameters, in particular the energy density, is an ongoing
research in the field of electrochemical energy storage. Recently the 'Li-rich' layered
transition metal oxides (LLTMOs), of general formulation Li[LixM1-x]O2, used as cathode
materials were shown to be promising for increasing energy density of Li and Na ion
batteries. In this systems M in the metallic layer is partially substituted by Li, which enables
a cumulative cationic (M4+/M5+) and anionic (2O2-/(O2)n- oxo to peroxo transformation) redox
activity, thus increasing the capacity[1-3]. However, the oxidation of oxygen can lead to
irreversible structural transformations, voltage hysteresis or even oxygen release, which
preclude LLTMO-cathodes from commercialization. Recent theoretical results suggest that
the electronic ground state of the lithiated oxide (Mott-Hubbard or charge transfer) [4] is an
important parameter that govern the mechanism of the anionic process in charge.
Nonetheless, no clear consensus has yet been reached on the reversibility of the anionic
process and the associated structural reorganization of the oxygen network.
In our work, we want to answer whether the X-ray absorption spectroscopy (XAS)
can be a technique of choice to address this question. In the X-ray absorption
spectroscopy the core electron of a chosen atom is excited to the available unoccupied
states with well defined symmetry and therefore any variations in the electronic and the
local structure of LLTMO upon cycling can be seen in the measured spectrum. We used
density functional theory (DFT) methods and its DFT+U variant to simulate the XAS
spectra for different LLTMOs displaying different electronic ground state and followed the
XAS evolution at various delithiation stages. We will show that true peroxides (O 2)2-
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species at 1.5 A cannot be stabilized in these compounds when oxygen is surrounded by a
transition metal. This is correlated to the charge transfer gap of oxides with respect to O2-/
(O2)2- redox couple. This rationalization allowed us to propose M/M' chemical substitutions
that can limit or suppress these irreversibilities. Moreover, our approach allowed us to
benchmark various DFT methods in their ability to reproduce XAS spectra and to check
their transferability.
1 M. Saubanère, E. McCalla, J.-M. Tarascon and M.-L. Doublet: Energy Environ. Sci., 9, 984-991 (2016).2 Y. Xie, M. Saubanère and M.-L. Doublet: Energy Environ. Sci., 10, 266-274 (2017).3 M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezi , M. T. Sougrati , M-L. Doublet, D. Foix, D.
Gonbeau, W. Walker, A. S. Prakash, M. Ben Hassine, L. Dupont and J-M. Tarascon: Nature Materials, 12,
827–835 (2013).4 M. Ben Yahia, J. Vergnet, M. Saubanère and M.-L. Doublet, Nature Materials (2019).
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Effect of Cs doping on optical absorption of APbI3 (A =
-CH3NH3, -CH(NH2)2) hybrid lead iodide perovskites
Ankur Taya and Manish K. Kashyap Department of Physics, Kurukshetra University, Kurukshetra-136119 (India)
e-mail address: [email protected], +91-9050851609
Keywords: Density Functional Theory, hybrid halide perovskite, solar cells
Abstract
A Hybrid lead halide perovskites solar cells (PSCs) have shown tremendous potential
as a major player in future solar domain. Suitable band gap, high absorption and
stability are the vital factors for ensuring enhanced photon conversion efficiencies
(PCE) of these materials. Cation substitution is an effective tool to tune the desired
properties of perovskite materials [1]. In this work, we have studied the effect of Cs
doping on structural, electronic and optical properties of formamidinium lead iodide
CH(NH2)2PbI3 (FAPBI3) and methyl ammonia lead iodide CH3NH3PbI3 (MAPbI3) by
first-principles approach. Our calculations reveal that 12.5% Cs substitution in
MAPbI3 /FAPBI3 slightly increases the band gap in both materials to 1.62 eV/ 1.47 eV,
whereas an enhanced optical absorption in visible region of solar spectra is observed
only in FAPbI3. Further, the analysis of formation energy manifests the significant
stabilization of Cs:FAPbI3, making it one of the promising candidates for high
efficiency PSCs at ambient environmental conditions.
References
1D. H. Ji, S. L. Wang, X. Z. Ge, Q. Q. Zhang, C. M. Zhang, Z. W. Zeng & Y. Bai, Physical Chemistry Chemical Physics 19, 17121 (2017).
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Probing interactions at polymer/ZnO interfaces through a dialogue between quantum modelling, conceptual DFT and experiment
Jan Turek,a* Sam De Waele,b Stefaan Cottenier,b Herman Terryn,c Frank De Profta *Email: [email protected], Phone: +3226293520
aEenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel, Pleinlaaan 2, Brussels 1050, Belgium
bCenter for Molecular Modeling, Ghent University, Technologiepark 903, 9052 Zwijnaarde, Belgium
cResearch Group Electrochemical and Surface Engineering (SURF), Vrije Universiteit Brussel, Pleinlaaan 2, Brussels 1050, Belgium
Interfaces, Zinc Oxide, Periodic DFT, Conceptual DFT
Abstract The durability of hybrid polymer/metal systems and the enhancement of their
functional properties is one of the biggest challenges in materials chemistry and
engineering. Polymer adhesives bonded to metallic substrates appear in a variety of
situations, from corrosion protective paints and varnishes in automotive and
aerospace industries, protective coatings for microelectronics, to wear-resistant
biocompatible coatings in biomedicine and non-toxic interior coatings in food or
beverage cans.1 In addition to adhesive joints, organic coatings are used in the
aforementioned industries and in construction in order to protect the underlying
substrate against atmospheric influences.2 Therefore, the major requirement for
these adhesive joints and coatings is to withstand mechanical forces, changes in
temperature and long-time exposure to corrosive environments.3
The interfacial chemical interactions between the organic and metallic layers were
suggested to be the key players in the performance and durability of these hybrid
systems.4 The main problem in the experimental investigation of polymer adhesion
on metallic substrates is the limited accessibility of the nanometre-thin interface,
which is covered by micrometre-thick polymer over layers (Figure 1).5
Figure 1. Schematic view of the polymer/metal hybrid systems.
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The main goal of the presented work is to investigate the adhesion properties of hybrid
polymer/zinc systems, which are largely determined by the interactions between the
zinc (hydr)oxide and organic layers occurring at the so-called buried interface. To this
end, state-of-the-art computational and interpretative quantum chemical methods are
applied, and the obtained results are validated with the experimental data provided by
the experimental partner. The combination of theoretical and experimental data will
eventually lead to a more fundamental understanding of the interactions at
polymer/metal interfaces.
References
1W. Brockmann, P. L. Geiss, J. Klingen, K. B. Schroder, B. Mikhail, Adhesive Bonding: Adhesives, Applications and Processes; Wiley-VCH: Weinheim (2008). 2A. Kakaroglou, B. Nisol, T. Hauffman, I. De Graeve, F. Reniers, G. Van Assche, H. Terryn, Surf. Coatings Technol. 259, 714 (2014). 3J. Wielant, T. Hauffman, O. Blajiev, R. Hausbrand, H. Terryn, J. Phys. Chem. C 111, 13177 (2007). 4H. Leidheiser, P. D. Deck, Science 241, 1176 (1988). 5P. Taheri, M. Ghaffari, J. R. Flores, F. Hannour, J. H. W. De Wit, J. M. C. Mol, H. Terryn, J. Phys. Chem. C 117, 2780 (2013).
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Electronic Structure Calculations of MAPbI3 and MASnI3 Hybrid Perovskite Solar Cells
Cameron Underwood, J. David Carey, S. Ravi P. Silva
Advanced Technology Institute, GU2 7XH, Guildford, United Kingdom
[email protected] +44 (0)1483 686102
Keywords: DFT, VASP, Perovskite, Hybrid, Solar Cell
Abstract
Perovskite solar cells (PSCs) have made unprecedented advancements since their
rapid emergence in 2009, increasing in efficiency from 3.8% to 24.2%1 in 2019.
These are currently able to compete with the efficiency of silicon solar cells used
worldwide at a fraction of the cost. As these cells are still relatively young there are
still a wide selection of problems which need to be overcome before these are readily
available worldwide, there is also a wide selection of gaps in the theory behind these
new solar absorber materials. Density Functional Theory (DFT) is a quantum
mechanical ab-initio technique which can be used to study the structural and
electronic properties of these materials to fill in the current gaps in theory with the
eventual aim of being able to mass produce PSCs.
Structural and electronic calculations have been made on MAPbI3 and MASnI3 using
PBE + SoC with close benchmarking to experimental results, these include full partial
density of states analysis. A k-point spacing convergence issue has been noted here
with regards to the direct-indirect nature of the bandgap when calculating the
bandstructure of the material, this has been analysed to avoid analogous bandgap
behaviour results.
A key area of current Perovskite solar cell research is the removal or reduction of
toxic lead from the system, a notable method has been by partially replacing lead
with tin, this has had the best success to date with efficiencies of 20.2%2 noted for
this low bandgap absorber. Progress has been made in DFT calculations of lead-tin
mixed Perovskite structures, with some simple MAPbxSn1-xI3 supercell structures
tested, again using PBE + SoC including a partial density of states consideration.
References
1 NREL, Best Research-Cell Efficiency Chart (2019). 2 J.Tong et al, Science 364,6439 (2019): 475-479.
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Infinite carbon chains sandwiched by copper monolayers:
novel 2D Cu2C
Busheng Wang and Gilles Frapper [email protected]; +33 (0)6 65 22 41 59
1Applied Quantum Chemistry group, E4, IC2MP, UMR 7285 Poitiers university-CNRS, 4 rue Michel Brunet TSA 51106 - 86073 Poitiers Cedex 9, France.
Keywords: structural prediction, nanomaterial, carbon chains, dirac cones, stability.
Abstract
Recently, two-dimensional (2D) Dirac material Cu2Si has been theoretically predicted
and experimentally observed1,2. By using evolutionary algorithmstructure technics
(USPEX code3) combined with first-principles calculations (VASP code4), we report
the prediction of Cu2C with infinite carbon chains sandwiched by copper monolayers,
a brain new 2D structure.
Figure 1. Crystal structure of Cu2C (space group: P2/c; unit cell: 6 atoms; distances in Å).
First principles calculations and molecular dynamics indicate that this two-
dimensional cristalline Cu2C structure is dynamically stable, and survives brief 10 ps
annealing up to 600 K. Moreover, this phase exhibits Dirac cones with massless
Dirac Fermions. The unique electronic structure renders this 2D Cu2C a promising 2D
material for application in nanoelectronics.
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Our research was supported by PRCI ANR-NSFC Predict_2D_Nanomat. The calculations were performed at the supercomputers GENCI (Grant n° A0060807539) and Mésocentre SPIN of Poitiers U.
References
1L. M. Yang, V. Bacic, I. A., Popov, A. I. Boldyrev, T. Heine, T. Frauenheim, and E. Ganz, J. Am. Chem. Soc. 137, 2757 (2015). 2Feng B, Fu B, Kasamatsu S, Ito S, Cheng P, Liu CC, Feng Y, Wu S, Mahatha SK, Sheverdyaeva P, Moras P. Nat. commun. 18,1007 (2017). 3A. R. Oganov and C. W. Glass, J. Chem. Phys. 124, 244704 (2006); C. W. Glass, A. R. Oganov and N. Hansen, Comput. Phys. Commun. 175, 713–720 (2006). 4G. Kresse and J. Furthmuller, Phys. Rev. B 54, 11169 (1996); G. Kresse and J. Furthmuller, Comput. Mater. Sci. 6, 15 (1996).
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TALEBI HABIBABADI Amir Hossein
University of Luxembourg
TALLA NOUTACK Martin
CEA Cadarache
TAUDUL Beata
Universite de Montpellier
TAYYEBI Ebrahim
University of Iceland
THAL Maike
Technische Universitat Chemnitz
THYGESEN Kristian
Technical University of Denmark
TISSIER Roger-Charles
Universite d’Aix-Marseille
TRANCA Ionut
Eindhoven University of Technology
TUREK Jan
Vrije Universiteit Brussel
UNDERWOOD Cameron
University of Surrey
VALENCIA Hubert
Nagoya University
VON WEDELSTEDT Alexander
HTW Dresden
WADHWA Payal
Indian Institute of Technology Ropar
WANG Busheng
University de Poitiers
WANG Junjie
Northwestern Polytechnical University
WANG QI
Universite de Rennes
WAZZAN Nuha
University of Melbourne
WAZZAN Nuha
King Abdulaziz University
WEI Jianyu
Universite de Rennes
WHANGBO Mike
NC State University
ZAHARIEV Tsvetan
Bulgarian Academy of Sciences
ZANCA Federica
University of Sheffield
ZHANG Heng
Universite de Poitiers
ZIEMBICKI Jakub
Wroclaw University of Science and Technology
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