1. Lecture 7 DFT Applications
武晓君 江俊

2. Why DFT

3. DFT Application

4. DFT Application

5. DFT Application

6. DFT Application EA IP WF Strict in DFT theory,
but not strict in DFT computations.

7. DFT Application
For Solid State Physics

8. DFT Application
For Molecular Electronics

9. Quantized electron energy Extended π systems Elegance
The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed — a development which I think cannot be avoided.
Richard Feynman
Molecular Electronics: Use molecule to conduct electrons and thereby perform electronic processing
Size: scale from 1 to 100 nm
Given the same amount of space, many times faster and more powerful than silicon based devices
Manufacturing:
fabricated identically and defect-free in enormous numbers
Self-assembly Manufactured
molecular synthesis tools highly developed
Quantized electron energy
Extended π systems
Provides thermodynamically favorable electron conduction
π Conjugation acts conduction switch
Elegance
Elegant solutions to non-volatile and inherently digital storage

10. FET
SWCNT across Pt Electrodes (C. Dekker, Delft)

11. Electron transport in molecular device
HOMO

12. Theoretical Modelling for Molecular Electronics
Quantum Chemistry
Most cost-effective way to treat molecular system
Solid State Physics
Bulk Materials
Molecular Device ?
Different Effects
Huge Success
Green Functional theory.
Still Difficult !!! S D
Surface adsorber +
non-equilibrium
Green’s function M

13. Landauer Formula Landauer Formula
DOS Ef
- Treat the “extended molecule” with Quantum Chemistry
- Describe the electrode with Density of States (DOS)
- The extended molecule is in equilibrium with the
source and drain by lining up the effective Fermi level
Tunneling Current Density from Source to Drain:

14. Quantum Chemistry approach based on Green’s Function Theory

15. Quantum Chemistry approach based on Green’s Function Theory

16. Quantum Chemistry approach based on Green’s Function Theory
Based on Elastic-Scattering Green’s Function Theory
Transition operator:
Transition Probability:

17. Landauer Formula Tunneling Current Density from Source to Drain: DOSEf

18. Electronic transport in Gold-Benzenedithiol-Gold
Simulation Results
Current vs. Voltage and Conductance vs. Voltage

19. Conjugated Polymer Increasing of size, Density of State(DOS) increases
Biggest one:
3200 atoms
13440 electrons
20000 Basis functions(6-31G)
Increasing of size, Density of State(DOS) increases
Discrete molecular orbital to continuous band
HOMO-LUMO gap remains constant as 2.78eV
Energy structure analogous to inorganic Semiconductor

20. Conjugated Polymer
Semiconducting behaviour, verified by Experiments.

21. poly 24 = 18.3 nm i(Ei) =i(0)(1+ Ei)  is the dephasing factor
Poly10, Charging effect
poly 24 = 18.3 nm
i(Ei) =i(0)(1+ Ei)
 is the dephasing factor
A: =3, B: =10

22. Electronic transportation in (5, 5) CNT

23. Electronic transportation in (5, 5) CNT
PNAS, 101,13408,2004

24. Molecular Field Effect Transistor
Gate Bias (Vg) Modulate the transportation of electrons

25. Current-Voltage characteristics, IETS Simulation of Carbon Nanotube (CNT), DNA, ...
Structure determination, DNA sequence identification, Bio-molecular devices

26. Vd Vd IETS: Inelastic Electron Tunneling Spectroscopy
The Fingerprint of Molecular Devices
Vibration of molecule leads to transition peak Vd Vd

27. IETS Measure
The Fingerprint of DNA
Vibration of DNA leads to transition peaks

28. Thanks!