Questaal & phonopy calculation

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Questaal & phonopy calculation#

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

The interface uses the site files. Such files have only a small amount of information within them relating to the calculation. Extention to support ctrl files is planned.

How to run#

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

  1. Setup an lmf calculation with external site file instead of a site section in the ctrl file. Both relative and cartesian coordinates are supported. Remember to set forces=1 in section ham of the ctrl file.

  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. The original alat present in site.lm is preserved. 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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