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, e.g.,

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

3. Rename SPOSCAR created in (2) to POSCAR (POSCAR-{number} and phonopy_disp.yaml files will never be used.)

   % mv SPOSCAR POSCAR
   

4. Calculate force constants of the perfect supercell by running VASP with IBRION = 8 and NSW = 1. 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.
   

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

   % phonopy --fc vasprun.xml
   

6. Run phonopy with the original unit cell POSCAR-unitcell and setting tag FORCE_CONSTANTS = READ or --readfc option, e.g., as found in example/NaCl-VASPdfpt

   % phonopy --dim="2 2 2" -c POSCAR-unitcell band.conf
           _
     _ __ | |__   ___  _ __   ___   _ __  _   _
    | '_ \| '_ \ / _ \| '_ \ / _ \ | '_ \| | | |
    | |_) | | | | (_) | | | | (_) || |_) | |_| |
    | .__/|_| |_|\___/|_| |_|\___(_) .__/ \__, |
    |_|                            |_|    |___/
   
                                        1.1
   
   Band structure mode
   Settings:
     Force constants: read
     Supercell:  [2 2 2]
     Primitive axis:
        [ 0.   0.5  0.5]
        [ 0.5  0.   0.5]
        [ 0.5  0.5  0. ]
   Spacegroup:  Fm-3m (225)
   Paths in reciprocal reduced coordinates:
   [ 0.00  0.00  0.00] --> [ 0.50  0.00  0.00]
   [ 0.50  0.00  0.00] --> [ 0.50  0.50  0.00]
   [ 0.50  0.50  0.00] --> [-0.00 -0.00  0.00]
   [ 0.00  0.00  0.00] --> [ 0.50  0.50  0.50]