COMPUTATIONAL PHYSICS

Aniket Bhattacharya 1 GS + 1UGSArchana Dubey -Abdelkader Kara 1 UGSTalat Rahman 7 GS + 1 REU + 5.2 PostDocsPatrick Schelling 2 GS + 1UGS + 3 REUSergey Stolbov 1GS

~ 30 papers in the last 12 months

Research: multi-tools to study physical and chemical propertiesof materials at different time and length scales.

Development: new tools to extend the accuracy and speed of simulations to larger length and time scales

Abdelkader KARA RESEARCH

Organic Materials SilicenePentacene/Cu(110)

Adsorption energy: 1.49 eV

Diffusion barrier: 150 meVSexithiophene on Ag(110)

Azimuthal angle (degrees)

(E-E

F)

(eV

)

0.7 ML

0.8 ML

1 ML

Experiment

Pentacene on p(2x1)O /Cu(110)

[0 0 1] [1 1 0]

Charge transfer

Diffusion barrier: 66 meV

akara@mail.ucf.edu www.physics.ucf.edu/~kkara

Nano-Ribbons: Si/Ag(110)

Confinement

Side view

Interface states : theory and

Abdelkader KARA DEVELOPMENT

Self-Learning Kinetic Monte CarloIn collaboration with Rahman’s group On Lattice Recognition

Gain in Speed and Precision

Go over all atoms andGo over all atoms and determine all processesdetermine all processes

which are possible.which are possible.

ΓΓ(i) (i) == ΓΓoo(i)(i)exp(-ΔEexp(-ΔE(i)(i) /k /kBBTT)) get two randomget two random

numbers rnumbers r11, r, r22

from [0,1[from [0,1[

Do process “k”, i.e.Do process “k”, i.e.move one atommove one atom

(randomly chosen)(randomly chosen)

adjust the clock:adjust the clock:1/R1/R

Calculate R = Calculate R = ΣΓΣΓ(i) (i)

and find process “k” and find process “k” from the data base:from the data base:

ΣΣkk Γ Γ(i) (i) > > r r11R >R > ΣΣk-1k-1ΓΓ(i)(i)

If novel If novel ConfigurationConfiguration

occurs: occurs:

Calculate Calculate ∆∆EE

yes

noData baseData base

StartStart

EndEnd

Off Lattice Recognition

Experiment SL-KMC simulation

1

01 1

/N N

i ji j

D

PREFACTORS

Tk

U

k

Snd

h

TkTD

B

vib

B

vibB expexp2

2

0

Concerted Motion

akara@mail.ucf.edu www.physics.ucf.edu/~kkara

Aim: Understanding of proteins and enzymes at functional levels.

Procedure: Hartree-Fock- Cluster procedure implemented by the Roothaan variational approach.

The model system to simulate deoxy hemoglobin consists of a heme unit with imidazole of the proximal histidine attached to the Fe atom on the heme unit through one of the two N in the imidazole,

namely the apex Nε in the figure.

Peripheral carbons of the pyrroles in the heme unit are terminated by H

atoms .

Fe atom is rather internal in the central region of the heme unit , and the adjustments made in the peripheral regions of the heme are not expected to influence the electron

distribution significantly in the neighborhood of the 57mFe nucleus .

Dr. Archana Dubey

QuickTime™ and a decompressor

are needed to see this picture.

Patrick K. Schelling, University of Central Florida

Multiscale simulation of mass and heat transport

NSF-DMR 0809015 NSF-REU 0755256

Multiscale simulation of laser ablation

Nanoscale thermal transport

Complex oxides and geophysics

Interfacial thermal transport and phonon dynamics

• Scattering simulation/theory• Transport in nanocrystalline materials

• Effect of discrete phonon spectra• Size-dependence of interfacial resistance

• Atomistic models with excited electrons• Electron-phonon scattering• Combined phonon/electron transport

• Oxides for thermal barrier coatings• Point-defect scattering, disorder• Transport in MgSiO3 up to p=120GPa

Cross-sectional viewof simulated Si nanowires

Phonon scatteringat Si grain boundary

First principles studies of stability and reactivity of electro-catalysts for low-temperature fuel cells

Sergey Stolbov, Associate Professor, Physics Dept. UCF Stability: Search for new materials to replace unacceptably expensive Pt in electrodes of low-temperature

fuel cells (FC) is an important and challenging problem for electro-catalysis. Promising electro-catalysts such as Ru nanoparticles with the Pt (Pt/Ru) and Se (Se/Ru) sub-monolayer coverage have a complex

geometric structure that makes their stability an issue of concern. We apply the density functional theory (DFT) based computational approach to reveal key characteristics of stability of these materials.

We find that Pt atoms tend to join into large 2D

islands by making Pt-Pt and Pt-Ru covalent

bonds, while Se atoms charged by electron

transfer form the surface repeal and hence prefer

stay apart from each other on the substrate .

Island formation energy per/atom of Pt (right panel) and Se (left panel) as a function of the island size

Work in progress :.1In collaboration with M. Alcantara Ortigoza and T. S. Rahman we are studying electronic structure and

energetics of layered Ru/Pt and Ru/Pt/Ru structures to explain character of growth of such structures observed in experimental works by R.J. Behm and co-workers (Vacuum 84, 13 (2010), Surf. Sci. 603, 2556 (2009)) .

.2With graduate student S. Zuluaga we begun studying geometric and electronic structures of Se-Ru nano-clusters.

M. Alcantara Ortigoza, S. Stolbov and T. S. Rahman, PRB, 78, 195417 2008

Pt/Ru Se/Ru

S. Stolbov, in preparation