Hands on Session: Localized vibration mode

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Hands on Session Localized vibration mode
Jiraroj T.thienprasert
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Overview

• Localized vibration mode
• DYNAMIC METRIX (Using frozen phonon method)
• PERTURBATION METHOD
• Fit to potential curve
• Perturbed Matrix
• GaAs Doped with N
• ZnO Doped with N

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DYNAMIC MATRIX
required script vaspDYNAMIC, vaspFORCEMATRIX
run.dynamic.N and run.dynamic.P After relaxing
GaAs doped with N to find minimum volume or
lattice constant, then relax bulk GaAs doped with
N again in order to get all force less than 1E-4
by using the following INCAR ,
INCAR System GaAs_N ENCUT 452 ! required
energy cutoff PREC ACCURATE ! avoid wrap around
errors EDIFFG -1E-4 ! All force less than
1E-4 EDIFF 1E-6 ! high accuracy
required IBRIONS 5 ! finite differences LREAL
.FALSE. ! reciprocal space projection
technique ALGO FAST ! fast determination of
ground state
For large supercell LREAL .TRUE.
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DYNAMIC MATRIX
Make KPOINTS and POSCAR files.
KPOINTS K-Points 0 Monkhorst Pack 4 4
4 0 0 0
POSCAR GaAs doped with N (Zinblend) 5.299 1.0
0.0 0.0 0.0 1.0 0.0 0.0 0.0
1.0 8 Direct (or Cartesian) xxx xxx xxx
GaAs, doped with N, is relaxed to make all force
lt 1E-4
POTCAR file contains information of N, As and Ga
atoms.
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DYNAMIC MATRIX
After running vasp, we get CONTCAR which is
relaxed until all force less than 1E-4 (EDIFFG),
then use vaspD2C to convert the CONTCAR file to
Cartesian type. Use script vaspDYNAMIC to
generate POSCAR files which is used to run vasp.
After getting POSCAR files,generated from
vaspDYNAMIC, then use following script to run
frozen phonon method.
Move all atom from equilibrium position with
0.01 a in x, y and z direction ( a is lattice
con-stant)
Script run run.dynamic.P run.dynamic.N
!!! Dont forget to check number of atom (N) in
run.dynamic.P and run.dyamic.N script !!!
2 Dimension
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DYNAMIC MATRIX
When running vasp finish, we get 2 files that is
OUTCAR-P and OUTCAR-N. Then we use script
vaspFORCEMATRIX to make DYNAMIC MATRIX. We
can use MATHEMATICA or fortran77 program to
calculate the vibration frequency. (Please
contact Mr.Jiraroj T.thenprasert to obtain these
programs chorawut_at_gmail.com)
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PERTURBATION METHOD
How to calculate vibration frequency from the
potential curve ? First we must relax bulk GaAs
doped with N to minimize volume and force acting
on atoms. Then we extend and compress position of
Nitrogen and create new POSCAR files.(POSCAR-P01,
POSCAR-P02, and POSCAR-N01, POSCAR-N02, )
After that running vasp with following INCAR and
KPOINTS to find the energy at each Nitrogen
position and then plot energy Vs displacement of
Nitrogen from equilibrium. Now we get the
parabola curve and then fit these curve with
polynomial order 4
INCAR System GaAs_N ENCUT 452 ! required
energy cutoff EDIFF 1E-6 ! high accuracy
required ISMEAR0 IBRIONS 2 NSW0
KPOINTS K-Points 0 Monkhorst Pack 4 4
4 0 0 0
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PERTURBATION METHOD
We can use script to generate POSCAR-P01 , P02,
P03, and POSCAR-N01, N02, N03, ... (P and N are
extend and compress)
!!! Use script run.h to run automatic. !!!
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PERTURBATION METHOD
Fit to polynimial order 4
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