[SOLVED]Phonon dispersion with negative frequency

Dear all,

I modified the files from DFPT tutorial and wanted to generate the phonon dispersion of bulk VSe2. However, the result looks really strange with negative frequency (energy). I checked my inputs several times to see whether they satisfy VSe2, but I couldn’t find it.
Hope someone can help my problem. Thank you!

Here are my steps:

  1. Run abinit VSe2_1_1.abi >log 2>err &
    VSe2_1_1.abi (5.8 KB)

  2. Run mrgddb < VSe2_1_3.abi to combine all DDB files
    VSe2_1_3.abi (903 Bytes)

  3. Run anaddb < VSe2_1_5.files > VSe2_1_5.log
    VSe2_1_5.abi (5.7 KB)

  4. Run abiopen.py trf2_5_PHBST.nc --expose --seaborn=talk to plot the phonon dispersion bands

The error is here:

rfatpol   1 2        # Treat displacements of all atoms

you have 3 atoms in the unit cell so

rfatpol   1 3        # Treat displacements of all atoms

From the documentation of rfatpol

For the calculation of a full dynamical matrix, use rfatpol (1)=1 and rfatpol (2)=natom, together with rfdir 1 1 1.

Dear gmatteo,

Thank you so much for helping me again and pointed this out! However, after corrected rfatpol and modified my VSe2_1_5.abi (2.9 KB), I still get the negative frequency as shown below. Is there anything I didn’t notice as well?

Screen Shot 2021-11-01 at 11.13.00 AM

Best regards,

Hi @gmatteo ,

The problem was solved after I changed occopt to the value other than 0 and 1. Thanks for your help!

Best regards,