Siesta & phonopy calculation¶

Supported Siesta tags¶

Currently phonopy can read the siesta tags listed below. More tags may be supported on request.

AtomicCoordinatesFormat, ChemicalSpeciesLabel, AtomicCoordinatesFormat,
AtomicCoordinatesAndAtomicSpecies, LatticeVectors

The procedure of a Siesta-phonopy calculation is the following:

Read a Siesta input file and create supercells with --siesta option:
```
% phonopy --siesta -d --dim="2 2 2" -c Si.fdf
```
In this example, 2x2x2 supercells are created. supercell.fdf and supercell-xxx.fdf (xxx are numbers) give the perfect supercell and supercells with displacements, respectively. In these supercell files, lines only relevant to crystal structures are generated. phonopy_disp.yaml is also created. This file contains information on displacements. Perhaps the supercell files are stored in disp-xxx directories, then Siesta calculations are executed in these directories.
Calculate forces on atoms in the supercells with displacements. Calculation specification tags have to be added to supercell-xxx.in files. Crystal structure is not allowed to relax in the force calculations, because atomic forces induced by a small atomic displacement are what we need for the phonon calculation.
Create FORCE_SETS by
```
% phonopy --siesta -f disp-001/Si.FA ...
```
Here *.FA files are the forces files created by Siesta. To run this command, phonopy_disp.yaml has to be located in the current directory because the atomic displacements are written into the FORCE_SETS file. An example is found in example/Si-siesta.

Run post-process of phonopy with the Siesta input file for the unit cell used in the step 1:

% phonopy --siesta -c Si.fdf -p band.conf

or:

% phonopy --siesta -c Si.fdf --dim="2 2 2" [other-OPTIONS] [setting-file]