Amset phonon-frequency calculation for polar materials

AMSET
1

Dear Alex,

I’m encountering some confusion regarding how to correctly prepare inputs for the “amset phonon frequency” command when working with polar materials in VASP.

In the AMSET documentation it is written that “The dielectric constants and polar phonon frequency can be extracted from the VASP outputs using the command:

amset phonon-frequency

The command should be run in a folder containing thevasprun.xmlandOUTCARfile output from the DFPT calculation. For polar materials, anOUTCARfrom the NAC calculaiton must be provided instead”

However, in practice, this raises a few issues:

  1. Two OUTCAR files?
    There are two OUTCAR files

    • OUTCAR from phonon calculation (IBRION=6 and LPHON_DISPERSION = .TRUE.)

    • OUTCAR from a separate LEPSILON = .TRUE. calculation (for Born charges and dielectric tensor)

    Since both files are named OUTCAR, it’s unclear which one AMSET expects in the working directory.

  2. Using OUTCAR from DFPT calculation and LEPSILON = .TRUE.
    Even when I provide the OUTCAR from the LEPSILON calculation, which clearly contains:

    • Born effective charges

    • dielectric tensor

    I still get the warning: “No NAC corrected file provided. Skipping calculation requiring NAC”.

  3. Using OUTCAR from phonon calculation with IBRION=6 and LPHON_DISPERSION = .TRUE.
    I am getting errors, which is not giving any phonon-frequency value.

So what are the correct files required for this calculation?

2

Hi Sayan,

You need the OUTCAR from the second calculation listed in the DFPT section in the documentation: Calculation Inputs - AMSET Documentation. I.e., the one with LPHON_DISPERSION and LPHON_POLAR.

Best,
Alex