Elk & phonopy calculation#

Supported Elk tags#

Currently Elk tags that phonopy can read are shown below. More tags may be supported on request.

atoms, avec, scale, scale1, scale2, scale3

A procedure of Elk-phonopy calculation is as follows:

Read an Elk input file and create supercells with --elk option:
```
% phonopy --elk -d --dim="2 2 2" -c elk-unitcell.in
```
In this example, 2x2x2 supercells are created. supercell.in and supercell-xxx.in (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 of supercell-xxx.in are stored in disp-xxx directories as elk.in, respectively, then Elk calculations are executed in these directories.
Calculate forces on atoms in the supercells with displacements. Calculation specification tags have to be added to each elk.in file. Crystal structure is not allowed to relaxed in the force calculations, because atomic forces induced by a small atomic displacement are what we need for phonon calculation.
Create FORCE_SETS by
```
% phonopy -f disp-001/INFO.OUT disp-002/INFO.OUT  ...
```
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. See some more detail at Elk interface. An example is found in example/Si-elk.

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

% phonopy --elk -c elk-unitcell.in -p band.conf

or:

% phonopy --elk -c elk-unitcell.in --dim="2 2 2" [other-OPTIONS] [setting-file]