Questaal & phonopy calculation

Questaal & phonopy calculation#

This is a tutorial for the interface between phonopy and Questaal https://www.questaal.org/.

Supported LM tokens#

    XPOS, ATOM, ALAT, PLAT

The interface uses LM suite site files. Such files have only a small amount of information within them relating to the calculation. At present, the interface requires the use of fractional co-ordinates. Since phonopy is capable of handling cartesian co-ordinates such an extension will be realised soon.

How to run#

The following is a walkthrough for a phonopy calculation with LM:

  1. Create a site file with the LM suite supercell maker, lmscell. For instance, use this command,

        echo 'm 1 0 0 0 1 0 0 0 1' | lmscell --wsitex ctrl.lm

    This will write site.lm to disk in the current directory. Note that this site file will be written in fractional co-ordinates. At present, the LM interface supports only fractional co-ordinates.

  2. Read the LM site file and create supercells with a command of the form,

        phonopy --qlm -d --dim='2 2 2' -c site.lm

    In this example, 2x2x2 supercells are created. supercell.lm and supercell-{id}.lm correspond to the perfect supercell and supercells with displacements, respectively. These supercell files are LM site files ready to be used in ctrl.lm. A file named phonopy_disp.yaml is also created in the current directory. This file contains information pertaining to displacements.

  3. Next, run the calculations for the generated displacements and be sure to use the --wforce=force flag. This will write a file containing forces. Phonopy will require this file to be read in the next step.

  4. Create FORCE_SETS by:

        phonopy --qlm -f supercell-001/force.lm supercell-002/force.lm  ...

    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.

  5. Run post-process of phonopy with the LM site file for the unit cell used in the first step

        phonopy --qlm -c site.lm -p band.conf

    or

        phonopy --qlm -c site.lm --dim="2 2 2" [other-OPTIONS] [setting-file]
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