VASP-DFPT & phonopy calculation

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VASP-DFPT & phonopy calculation#

How to run#

VASP can calculate force constants in real space using DFPT. The procedure to calculate phonon properties may be as follows:

  1. Prepare unit cell structure named, e.g., POSCAR-unitcell. The following structure is a conventional unit cell of NaCl.

     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

  2. Prepare a perfect supercell structure from POSCAR-unitcell,

    % phonopy -d --dim 2 2 2 -c POSCAR-unitcell

  3. For later convenience, it is recommended to generate phonopy_disp.yaml using SPOSCAR file,

    % phonopy -d --dim 1 1 1 --pa auto -c SPOSCAR

  4. Rename SPOSCAR created in (3) to POSCAR to be used in the VASP calculation.

    % mv SPOSCAR POSCAR

    POSCAR-{number} files will never be used.

  5. Calculate force constants of the perfect supercell by running VASP with IBRION = 8. An example of INCAR for insulator may be such like (just an example!)

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

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

    % phonopy --fc vasprun.xml

  7. Run phonopy

    % phonopy-load --readfc --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" -p

        _
  _ __ | |__   ___  _ __   ___   _ __  _   _
 | '_ \| '_ \ / _ \| '_ \ / _ \ | '_ \| | | |
 | |_) | | | | (_) | | | | (_) || |_) | |_| |
 | .__/|_| |_|\___/|_| |_|\___(_) .__/ \__, |
 |_|                            |_|    |___/
                                      2.26.6

Compiled with OpenMP support (max 10 threads).
Running in phonopy.load mode.
Python version 3.12.4
Spglib version 2.4.0

Crystal structure was read from "phonopy_disp.yaml".
Unit of length: angstrom
Band structure mode
Settings:
  Supercell: [1 1 1]
  Primitive matrix:
    [0.   0.25 0.25]
    [0.25 0.   0.25]
    [0.25 0.25 0.  ]
Spacegroup: Fm-3m (225)
Number of symmetry operations in supercell: 1536
Use -v option to watch primitive cell, unit cell, and supercell structures.

Force constants are read from "FORCE_CONSTANTS".
Force constants format was transformed to compact format.
Array shape of force constants: (2, 64, 3, 3)
Max drift after symmetrization by translation: -0.000000 (zz) -0.000000 (zz)

Reciprocal space paths in reduced coordinates:
[ 0.000  0.000  0.000] --> [ 0.500  0.000  0.000]
[ 0.500  0.000  0.000] --> [ 0.500  0.500  0.000]
[ 0.500  0.500  0.000] --> [ 0.000  0.000  0.000]
[ 0.000  0.000  0.000] --> [ 0.500  0.500  0.500]

Summary of calculation was written in "phonopy.yaml".
                 _
   ___ _ __   __| |
  / _ \ '_ \ / _` |
 |  __/ | | | (_| |
  \___|_| |_|\__,_|
    _images/NaCl-VASPdfpt.png

    When running with phonopy command, --readfc option is necessary:

    % phonopy --readfc band.conf
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