velph command

The velph command is a convenient tool for systematically performing electron-phonon interaction calculations using the VASP code and for analyzing the resulting data.

The velph command orchestrates the electron-phonon (el-ph) calculation workflow workflow by running a series of subcommands in a specific sequence.

velph subcommands

The velph command includes a variety of subcommands. To initiate an electron–phonon (el-ph) calculation, run velph init to generate the velph.toml file. Command options for velph init are detailed in velph init. Once the velph.toml file is prepared, other velph subcommands generate VASP input files, post-process VASP calculation results, and calculate derivatives of the local potential and PAW strengths with respect to atomic displacement, resulting in the phelel_params.hdf5 file. Most of the velph subcommands are explained in velph subcommands.

A typical workflow of velph subcommands for transport property calculation is illustrated below.

        graph LR
A[velph-init] --> B[velph-relax]
B --> C[velph-init]
C --> D[velph-nac]
C --> E[velph-el_bands]
F[velph-phelel]
D --> F
D --> H[velph-phono3py]
F --> G[velph-transport]
    

A list of supported subcommands is displayed by typing:

% velph
Usage: velph [OPTIONS] COMMAND [ARGS]...

  Command-line utility to help VASP el-ph calculation.

Options:
  -h, --help  Show this message and exit.

Commands:
  convert        Write velph.toml of velph 0.14 in the format of velph 0.15.
  el_bands       Choose electronic band structure options.
  el_dos         Choose electronic DOS options.
  generate       Write POSCAR-unitcell and POSCAR-primitive.
  init           Initialize an electron phonon calculation project.
  nac            Choose nac options.
  ph_bands       Choose phonon band structure options.
  ph_selfenergy  Choose ph_selfenergy options.
  phelel         Choose supercell options.
  phono3py       Choose phono3py options.
  phonopy        Choose phonopy options.
  relax          Choose relax options.
  scheduler      Show the job script _job.sh of each input set.
  selfenergy     Choose selfenergy options.
  transport      Choose transport options.

In the following example, two velph init command operations generate two different directories. The first operation performs crystal structure relaxation in the relax directory. The second operation, using the relaxed crystal structure, carries out additional calculations required for electron-phonon interactions in the calc directory. Details about velph-tmpl.toml are described in velph init template.

% ls
POSCAR-unitcell  POTCAR  velph-tmpl.toml
% velph init --template-toml velph-tmpl.toml POSCAR-unitcell relax
...
% cd relax
% velph relax generate
...
# Run VASP relaxation calculation
...
% cd ..
% ls
POSCAR-unitcell  POTCAR  relax/  velph-tmpl.toml
% velph init --template-toml velph-tmpl.toml `ls relax/relax/iter*/CONTCAR|tail -n 1` calc
...
% cd calc
% ls
POTCAR  velph.toml
% velph nac generate
VASP input files were written in "nac".
% ls
POTCAR  nac/  velph.toml
...
# Run NAC calculation
...
% velph phelel init
Displacement distance: 0.03
Number of displacements: 4
NAC parameters are read from "nac/vasprun.xml".
"phelel/phelel_disp.yaml" was written.
Run "velph phelel generate" to write the VASP input files.
% velph phelel generate
VASP input files were written in "phelel/disp-000".
VASP input files were written in "phelel/disp-001".
VASP input files were written in "phelel/disp-002".
VASP input files were written in "phelel/disp-003".
VASP input files were written in "phelel/disp-004".
% ls
POTCAR  nac/  phelel/  velph.toml
...