Generate VESTA mode files from VASP OUTCAR files

What this code does:

Automatically generates visualizations of vibrational modes computed from the density functional theory (DFT) code VASP, like this acoustic mode of ZrIN:

Details:

The file modes_to_vesta.py converts the modes calculated in a VASP density functional perturbation theory (DFPT) calculation (IBRION = 7 or 8) to the Visualization for Electronic and STructural Analysis VESTA file format. The final result is a VESTA file that allows you to visualize each vibrational mode computed from DFPT.

Usage:

In a single folder, include the following 4 files:

1. POSCAR, which gives the atomic positions and unit cell used as input to the DFPT calculation
2. OUTCAR, which should hold the results of an IBRION=7 or 8 calculation
3. poscar.vesta. This file is the direct result of opening the POSCAR file directly in VESTA and saving the file with the filename poscar and extension .vesta (note that poscar is lower-case). No modes/displacement vectors should be visible in VESTA prior to saving.
4. modes_to_vesta.py, which comes from this repo.

To run, do the following:

$  python modes_to_vesta.py <optional-vesta-filename>

Only the first two arguments are needed; the third argument is optional and can be used to specify an alternative VESTA filename (i.e., a name different from poscar.vesta)

The result is a set of 3N files where N is the number of atoms in the unit cell. Each file has the format mode_<freq>.vesta, where <freq> is the mode frequency in cm^-1.

Some parts of modes_to_vesta.py have been adapted from vasp_raman.py and Phonopy