How to calculate the Band Phonon structure using the Phonopy code (DFPT method)

 Phonopy code is developped to calculate the phonon and thermal properties plus some other functionalities.

To install the code click on the following link:

How to install Phonopy Code to calculate Phonon and Thermal properties

 

There are 2 ways to do phonon calculations which are:

1- Supercell method based upon finite differences technique

2- DFPT method based upon Density Functional Perturbative Theory

For more information check the following links:

https://www.vasp.at/wiki/index.php/Phonons:_Theory#Finite_differences

https://www.vasp.at/wiki/index.php/Phonons_from_finite_differences 

http://cmt.dur.ac.uk/sjc/thesis_prt/node39.html 

We will use the DFPT method and calculate the DOS and Band structure of NaCl. 

 
We need only the input files

 POSCAR-unitcell

Na Cl
   1.00000000000000
     5.6903014761756712    0.0000000000000000    0.0000000000000000
     0.0000000000000000    5.6903014761756712    0.0000000000000000
     0.0000000000000000    0.0000000000000000    5.6903014761756712
   4   4
Direct
  0.0000000000000000  0.0000000000000000  0.0000000000000000
  0.0000000000000000  0.5000000000000000  0.5000000000000000
  0.5000000000000000  0.0000000000000000  0.5000000000000000
  0.5000000000000000  0.5000000000000000  0.0000000000000000
  0.5000000000000000  0.5000000000000000  0.5000000000000000
  0.5000000000000000  0.0000000000000000  0.0000000000000000
  0.0000000000000000  0.5000000000000000  0.0000000000000000
  0.0000000000000000  0.0000000000000000  0.5000000000000000

INCAR

 PREC = Accurate
 ENCUT = 500
 IBRION = 8
 NSW = 1
 EDIFF = 1.0e-08
 IALGO = 38
 ISMEAR = 0; SIGMA = 0.1
 LREAL = .FALSE.
 ADDGRID = .TRUE.
 LWAVE = .FALSE.
 LCHARG = .FALSE.

 KPOINT

KPOINTS  
0
Gamma
18 18 6
0 0 0

 

Creation of POTCAR of SiO2 using POTCAR-Si and POTCAR-O

cat POTCAR-Si POTCAR-O > POTCAR

 

POTCAR-Si

POTCAR-O

 

2- Phonon calculations

 a- Prepare a perfect supercell structure from POSCAR-unitcell

% conda activate phonopy

(phonopy) % phonopy -d --dim="2 2 2" -c POSCAR-unitcell 

 

b- Rename SPOSCAR created in (a) to POSCAR (POSCAR-{number} and phonopy_disp.yaml files will never be used.)

(phonopy) % mv SPOSCAR POSCAR

 c- Doing scf calculation

(phonopy) % vasp_std

 

3- Calculation of sets of forces

 After finishing the VASP calculation, confirm vasprun.xml contains hessian elements, and then create FORCE_CONSTANTS:

% phonopy --fc vasprun.xml

Post-process

In the post-process,

1. Force constants are calculated from the sets of forces

2. A part of dynamical matrix is built from the force constants

3. Phonon frequencies and eigenvectors are calculated from the dynamical matrices with the specified q-points.

Band structure is calculated with the following setting file named, e.g., band.conf by:

ATOM_NAME = Na Cl
DIM = 2 2 2
PRIMITIVE_AXIS = 0.0 0.5 0.5  0.5 0.0 0.5  0.5 0.5 0.0
BAND = 0.0 0.0 0.0  0.5 0.0 0.0  0.5 0.5 0.0  0.0 0.0 0.0  0.5 0.5 0.5
FORCE_CONSTANTS = READ

The band structure is plotted by:

phonopy -c POSCAR-unitcell -p band.conf