CASTEP & phonopy calculation#

Examples to use phonopy with CASTEP as the force calculator are found at example/NaCl-castep and example/Cr-castep.

The followings are the copies of README contents in these example directories.

These are contriubted by @ladyteam.

NaCl-castep#

This is step-by-step example how to calculate phonon dispertion with CASTEP.

Generate supercell based on structrural parameters given in unitcell.cell file by running:
```
% phonopy -d --dim="2 2 2" --castep -c unitcell.cell
```
In this example file unitcell.cell contains initial spin values in positions_frac BLOCK. As well as the value of the U parameter in LDA+U approximation.
Use make_displ_dirs.sh bash script to make directories with input files needed to calculate FORCES for supercells.
```
% make_displ_dirs.sh supercell.param tail.cell
```
Please note file supercell.param is the standart CASTEP file with paremeters (convergence criteria, Ecut, functional name etc.). The file with name tail.cell contains k-mesh description, U parameter value, symmetry operation E, and name of pseudopotential.
Run CASTEP calculation in displ-001 directory

Generate FORCE_SETS file by running:

% phonopy --castep -f displ-001/supercell.castep displ-002/supercell.castep

Finally plot phonon bandstructure by running the following command:
```
% phonopy --castep -c unitcell.cell -p band.conf
```

This is step-by-step example how to calculate phonon dispertion with CASTEP. Spin-polarization example.

Generate supercell based on structrural parameters given in unitcell.cell file by running:
```
% phonopy -d --dim="2 2 2" --castep -c unitcell.cell
```
In this example file unitcell.cell contains initial spin values in positions_frac BLOCK. As well as the value of the U parameter in LDA+U approximation.
Use make_displ_dirs.sh bash script to make directories with input files needed to calculate FORCES for supercells.
```
% make_displ_dirs.sh supercell.param tail.cell
```
Please note file supercell.param is the standart CASTEP file with paremeters (convergence criteria, Ecut, functional name etc.). The file with name tail.cell contains k-mesh description, U parameter value, symmetry operation E, and name of pseudopotential.
Run CASTEP calculation in displ-001 directory

Generate FORCE_SETS file by running:

% phonopy --castep -f displ-001/supercell.castep

Finally plot phonon bandstructure by running the following command:

% phonopy --dim="2 2 2" --pa="-1/2 1/2 1/2 1/2 -1/2 1/2 1/2 1/2 -1/2" --castep -c unitcell.cell --band="1/2 -1/2 1/2 0 0 0 1/4 1/4 1/4" -p