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
E --> F
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:
  el_bands    Choose electronic band structure options.
  generate    Write POSCAR-unitcell and POSCAR-primitive.
  hints       Show velph command hints.
  init        Initialize an electron phonon calculation project.
  nac         Choose nac options.
  ph_bands    Choose phonon band structure options.
  phelel      Choose supercell options.
  phono3py    Choose phono3py options.
  phonopy     Choose phonopy options.
  relax       Choose relax options.
  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 made in "nac".
% ls
POTCAR  nac/  velph.toml
...
# Run NAC calculation
...
% velph phelel init
Found "nac" directory. Read NAC params.
"phelel/phelel_disp.yaml" was generated.
VASP input files will be generated by "velph phelel generate".
% velph phelel generate
VASP input files were generated in "phelel/disp-000".
VASP input files were generated in "phelel/disp-001".
VASP input files were generated in "phelel/disp-002".
VASP input files were generated in "phelel/disp-003".
VASP input files were generated in "phelel/disp-004".
% ls
POTCAR  nac/  phelel/  velph.toml
% velph phelel init
Found "nac" directory. Read NAC params.
"phelel/phelel_disp.yaml" was generated.
VASP input files will be generated by "velph phelel generate".
...

velph hints

This command provides a quick reference of calculation steps.

% velph hints