Using Phonopy with Wien2k

In this post I will describe how to calculate various phonon properties from Wien2k calculations, using Atsushi Togo's Phonopy program. As an example, I will use lithium hydride (LiH) which has a simple NaCl structure with a lattice constant of 4.01A (optimized in GGA approximation).

1. LiH has an fcc structure, but phonopy requires the P1 symmetry for Wien2k. So we convert LiH.struct to P1 by running x supercell and creating 1x1x1 cell with a type P. This cell should have 8 atoms - 4 Li and 4 H.

2. Create INPHON file with the following content:
ATOM_NAME = Li H
NDIM = 1 1 1
LSUPER = .TRUE.

The number of dimensions should be larger (e.g. NDIM 2 2 2), but for the testing purposes I've set it to 1 1 1. Then run:
phonopy --wien2k=LiH.struct

This creates the DISP file and several struct files with the supercells (in this particular case - LiH.structS, LiH.structS-001, LiH.structS-002. Having a look at the DISP file:
1 1 0 0
5 1 0 0

And having a look at LiH.structS-* files, one can see, that in these files atom 1 (Li) and atom 5 (H) are displaced by 0.01A in x direction. You can change the displacement manually, if you want.

3. Next step is to run two Wien2k calculations for LiH.structS-001 and LiH.structS-002 structure files, respectively, and save the resulting *scf files.

Important! The init for this calculations should begin from symmetry, e.g.:
init_lapw -b -s symmetry -vxc 13 -numk 100 -sp

This is important to start from symmetry because sgroup could reduce the symmetry, which will make phonopy unable to create a proper FORCES file. Also, the RMT spheres can overlap (check it with x nn!) and should be reduced if needed.

4. Once you have LiH001.scf and LiH002.scf from the above calculations, copy them in the directory with INPHON and DISP files, and run the following to generate FORCES:
phonopy --wien2k=LiH.struct -f LiH001.scf LiH002.scf

The order of scf files in this command should match the order of the atoms in DISP! If everything is ok, than the FORCES file will be saved and you can calculate various properties.

5. Backup INPHON to INPHON.1 and modify it for your needs as described in the phonopy manual. It is important that you comment or remove LSUPER=TRUE line. To calculate phonon DOS the new INPHON may look as follows:
ATOM_NAME = Li H
NDIM = 1 1 1
MP = 21 21 21

The phonon DOS can be calculated by invoking the command:
phonopy --wien2k=LiH.struct -p

References
1. Phonopy web page, where you may find the documentation.
2. Using phonopy with VASP (in Chinese, but readable with Google translate for non-speakers).