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Application of
Density Functional Theory
in
Molecular electronicsPedro Derosa
Fully non-local DFT Hamiltonian
22212
12111
21
HHHHHHHHH
M
M
MMMM
1 M 2
DENSITY FUNCTION THEORYDENSITY FUNCTION THEORY
GEOMETRY
MOLECULAR ORBITALS
CHARGE DISTRIBUTION
HAMILTONIANLEVEL OF THEORY: B3PW91/LANL2DZ
Efo
E
ELECTRONIC CONDUCTION THROUGH A ELECTRONIC CONDUCTION THROUGH A MOLECULE (cont...)MOLECULE (cont...)
Efo
E
Efo
E
From atoms to moleculesFrom atoms to molecules
Sigma bondPi bond
Diatomic molecule
Benzene ring
Au
L
H
HSC6H4SH Au-S-C6H4-S-Au
L
H H
L
Zero voltage Resonant Voltage
Valley Voltage
Zero voltage Resonant Voltage Valley Voltage
Cu
rren
tEn
ergy
Zero voltage Resonant Voltage
Valley Voltage
Zero voltage Resonant Voltage Valley Voltage
Cu
rren
tEn
ergy
RESONANT TUNNELINGRESONANT TUNNELING
SWITCHING BY CHARGINGSWITCHING BY CHARGING
NO2
NH2
S
NO2
NH2
S
NO2
NH2
S
NO2
NH2
S
Q=0 Q=-1 Q=-2
JPC B 105, 791 (2001)
JACS 122, 3015 (2000)
JCP 116, 1671 (2002)
Chen et al, SCIENCE 286, 1550 (1999)
SWITCHING BY CHARGINGSWITCHING BY CHARGING
NO2
NH2
S
NO2
NH2
S
NO2
NH2
S
NO2
NH2
S
0
5
10
15
20
0 1 2Voltage (V)
Cur
rent
( µA
)
NeutralAnion Dianion
0
5
10
15
20
0 1 2Voltage (V)
Cur
rent
( µA
)
NeutralAnion Dianion
60 K
0 K
0
5
10
15
20
0 0.2 0.4 0.6 0.8 1
Voltage (V)
Cur
rent
( µA
)
PlanarRotated
SAu
SAu
SAu
SAu
SWITCHING BY CONFORMATIONAL CHANGESSWITCHING BY CONFORMATIONAL CHANGES
0
100
200
300
400
500
0 1 2 3 4 5
JACS 123, 12418 (2001)
Q=0 Q=-1 Q=-2
THE SYSTEMSTHE SYSTEMS
-500
0
500
1000
1500
-5 -4 -3 -2 -1 0 1 2 3 4 5Voltage (V)
Cur
rent
(A
)
-200
2040
-2 -1 0 1
-500
0
500
1000
1500
-5 -4 -3 -2 -1 0 1 2 3 4 5Voltage (V)
Cur
rent
(A
)
-200
2040
-2 -1 0 1
µCURRENT vs. VOLTAGECURRENT vs. VOLTAGE
It behaves as a diode when ionized (anion and dianion)
Conducts poorly when neutral (insulator)
It is a programmable diode, ON when charged, OFF when neutral
+
-
NEUTRAL
ANION
DIANION
MOLECULAR ORBITALSMOLECULAR ORBITALS HOMO LUMO
