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

[Atsushi T. <atz...@gm...>]

Hi,

I recommend to use usual finite displacement approach but not DFPT.

Togo

On Mon, Feb 10, 2020 at 10:23 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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-- 
Atsushi Togo