Re: [Phonopy-users] [help] Query for translation imaginary modes taken into account by phonopy

[Alex K. <ake...@gm...>]

Dear Asif,

As prof. Togo should you should use finite displacement method. Also make
sure to use large enough super cell.

Also you should use --fc-symmetry option when plotting the phonon
dispersion. This may improve the translation invariance, and may improve
the phonon dispersion.


HTH...

Alex


On Mon, Feb 10, 2020, 2:23 PM BHATTI Asif <Asi...@ls...> wrote:

> Hello,
>
> I have a disordered structure and want to know the stability and thermal
> properties of the structure and this can be obtained through vibrational
> analysis.
>
> I optimized my structure with VASP until the forces were E=-1E-4. I used
> DFPT to obtain the Hessian matrix (for this aproach we don't need to build
> larger supercells). When I checked the OUTCAR there were three imaginary
> modes (the last three can be ignored because they are translationary
> modes). Now when I generate the FORCE_CONSTANTS using phonopy it takes into
> account these modes which can be seen in the DOS and BAND structure.
>
> Should I remove these imaginary translationary modes before submitting
> them to Phonopy? vasprun.xml doesn't display any imaginary modes only
> OUTCAR does.
>
> Is this the right procedure? The acoustic soft modes are flat near the
> Gamma point.
>
> NB: I am attaching a file so you can see where the problem is.
>
> Regards,
> Asif
>
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