VASP-DFPT & phonopy calculation

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-init -d --dim 2 2 2 -c POSCAR-unitcell

    This command writes SPOSCAR, phonopy_disp.yaml, and the displacement cells POSCAR-{number}. For VASP-DFPT, only the perfect supercell SPOSCAR is needed, and it will be used as POSCAR of the VASP calculation in the next step. The displacement cells POSCAR-{number} are not used here, whereas phonopy_disp.yaml is needed because it is read by phonopy in the post-process.

  3. Calculate force constants of the perfect supercell by running VASP with IBRION = 8. An example of INCAR for an insulator may look 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.

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

    % phonopy-init --fc vasprun.xml

  5. Run phonopy

    % phonopy --band auto -p
        _
 _ __ | |__   ___  _ __   ___   _ __  _   _
| '_ \| '_ \ / _ \| '_ \ / _ \ | '_ \| | | |
| |_) | | | | (_) | | | | (_) || |_) | |_| |
| .__/|_| |_|\___/|_| |_|\___(_) .__/ \__, |
|_|                            |_|    |___/
                                      4.3.1

-------------------------[time 2026-07-03 16:51:48]-------------------------
Rust backend (phonors) using rayon (10 threads).
Running in phonopy.load mode.
Python version 3.13.11
Spglib version 2.7.0

WARNING:
  primitive_matrix defaulted to 'auto' and was resolved to a non-identity
  matrix:
    [ 0.00000,  0.50000,  0.50000]
    [ 0.50000,  0.00000,  0.50000]
    [ 0.50000,  0.50000,  0.00000]
  This differs from phonopy v3, whose default was the identity matrix. Pass
  primitive_matrix='P' (or --pa P on the command line) to restore the v3
  behaviour.

Crystal structure was read from "phonopy_disp.yaml".
Unit of length: angstrom
Band structure mode (Auto)
Settings:
  Supercell: [2 2 2]
  Primitive matrix (Auto):
    [0.  0.5 0.5]
    [0.5 0.  0.5]
    [0.5 0.5 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 were read from "FORCE_CONSTANTS".
Force constants format was transformed to compact format.
Max drift after symmetrization by symfc projector: -0.00000000 (yy) -0.00000000 (yy)

SeeK-path is used to generate band paths.
  About SeeK-path https://seekpath.readthedocs.io/ (citation there-in)
Reciprocal space paths in reduced coordinates:
[ 0.000  0.000  0.000] --> [ 0.500  0.000  0.500]
[ 0.500  0.000  0.500] --> [ 0.625  0.250  0.625]
[ 0.375  0.375  0.750] --> [ 0.000  0.000  0.000]
[ 0.000  0.000  0.000] --> [ 0.500  0.500  0.500]
[ 0.500  0.500  0.500] --> [ 0.500  0.250  0.750]
[ 0.500  0.250  0.750] --> [ 0.500  0.000  0.500]

Summary of calculation was written in "phonopy.yaml".
-------------------------[time 2026-07-03 16:58:27]-------------------------
                _
  ___ _ __   __| |
 / _ \ '_ \ / _` |
|  __/ | | | (_| |
 \___|_| |_|\__,_|
    _images/NaCl-VASPdfpt.png

    phonopy reads FORCE_CONSTANTS automatically when the file is found alongside phonopy_disp.yaml. Settings can be supplied through a configuration file:

    % phonopy band.conf

Non-analytical term correction (Optional)#

Non-analytical term correction requires the Born effective charges and dielectric constant supplied through a BORN file (BORN (optional)). These are obtained from a separate VASP calculation with LEPSILON = .TRUE., and the BORN file can be generated with the phonopy-vasp-born auxiliary tool. The procedure is identical to the finite-displacement case; see VASP & phonopy calculation for details.