First%20Principle%20Electronic%20Structure%20Calculation

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First Principle Electronic Structure Calculation

• Prof. Kim Jai Sam (279-2077)

Students Lee Geun Sik, Yun So
Jeong
Lab. ??4-125 (279-5523)
http//ctcp.postech.ac.kr
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Our Research Area

• Optical property of nanocrystal (Yun)
• ? optoelectronics, biology
• Structural phase transition of crystal (Lee)
• ? most accurate calculation in phase
  transition
• Surface problem (Lee)

? All require electronic structure calculation of
crystal!
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Electronic structure calculation of crystal
It was impossible to solve many body problem
quantum mechanically.
But, with adiabatic approximation
(Born-Oppenheimer) and Density Functional Theory
(Hohenberg and Kohn 1964, Kohn and Sham 1965),
it became possible.
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Kohn-Sham total-energy functional
Kinetic energy of electron
Coulomb interaction between ion and electron
Coulomb interaction between electrons
exchange-correlation energy of electrons
static Coulomb interaction between ions

• DFT says that total energy is a unique functional
  of the electron density!
• Minimum energy is the ground state energy!

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Many electrons problem
Variational method
Self-consistent one-electron equation
(Kohn-Sham equation)
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Kohn-Sham equation
ion Coulomb potential
classical electronic Coulomb potential
exchange-correlation potential of electron gas
(LDA,GGA)
Minimize total energy functional
self-consistently!
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Approximations to the exchange-correlation
functional LDA and GGA
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Collection of functionals
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Self-consistent computational procedure
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Currently using simulation packages in our lab
VASP Pseudopotential, Ultra-soft, PAW, parallel
execution in supercomputer. ? studying CdSe
quantum dot system
SIESTA localized orbital basis and
pseudopotential, parallel execution,
very small basis, handle very large system
(nano system). ? studying now
WIEN97 LAPW method, parallel execution in
supercomputer. ? 9 publications since 2001,
mainly TiFe, TiFeH, TiFe(001) system.
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Surface electronic structure
TiFe (001)
Physical Review B, 65, 085410 (2002)
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Density of States
TiFe (001)
Physical Review B, 65, 085410 (2002)
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Surface band structure
TiFe (001)
Physical Review B, 65, 085410 (2002)
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Hydrogen adsorption on TiFe(001)
electron density of H/TiFe (001)
Int. J. Hydrogen Energy, 27, 403-412 (2002)
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Angular momentum projected density of states
H/TiFe (001)
Int. J. Hydrogen Energy, 27, 403-412 (2002)
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Topology of electronic band I
Ag2Se (SG19, P212121)
CMo2 (SG60, Pbcn)
J. Phys. Cond. 15, 2005-2016 (2003)
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Topology of electronic band II
PdSe2 (SG61, Pbca)
BFe (SG62, Pnma)
J. Phys. Cond. 15, 2005-2016 (2003)
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Parallelization of WIEN97 with MPI and SCALAPACK
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smaller memory usage with parallel execution!
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Parallelization of WIEN97 with MPI and SCALAPACK
II
shorter cpu time with parallel execution!
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Energy spectrum of nano structure
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Luminescent Materials I
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Quantum Dots (optical property)
CdSe quantum dot Diameter 4 nm
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TEM image CdS nanoparticles
HRTEM image of single CdS nanoparticle
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Photoluminescence of bare CdSe and coated CdSe
dots
Synthetic Metals, 139, 649-652 (2003)
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Applications in biology of optical quantum dots
10 distinguishable colors of ZnS coated CdSe QDs
Optical coding and tag based on emission
wavelength of ZnS coated CdS QDs
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Structural phase transition by ab initio method
Find the phase which minimize Gibbs free energy,
G E TS PV on (P,T) plane.
Pressure ? volume
Temperature ? entropy of phonon, harmonic
approximation
Helmholtz free energy requires phonon density of
states, g(?).
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Phonon band structure and density of states
MgO
Solid curve theoretical calculation Open circle
experimental result
J. Chem. Phys. 118, 10174 (2003)
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Pressure and Temperature phase diagram
J. Chem. Phys. 118, 10174 (2003)
MgO
B1NaCl structure B2CsCl structure
Theoretical results agree with experiments quite
well!
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Future Plan

• Quantum computing
• ? quantum dot is one of candidates for
  qubit.
• ? optical properties of quantum dot
• TDDFT (Time Dependent DFT)
• ? calculate electronic structure for excited
  states.
• Surface physics catalysis, hydrogen storage