[Pw_forum] Negative phonon frequencies?

[Eyvaz Isaev]

Dear Fredric,

Probably negative frequencies are due to lack of the
ASR not imposed for dynamic matrix calculations at the
\Gamma point. But they should not be too large. For
example, as it is mentioned in the PWSCF manual
(troubleshooting) it might be around 50cm^{-1} or
1.6THz.
Nevertheless, you have to be careful about your input
file. I remember, there was a mail from Gothenborg
(Sweden) where negative frequences for ZnS were
obtained due to an error in input file.
I suggest, it depends also on the pseudopotential
quality.

Regards,
Eyvaz.


--- Lu Frederic <lucre at ms1.hinet.net> wrote:
> Dear PWscf users,
> 
> While calculating phonon frequencies at Gamma of
> zb/wz GaN using
> PWscf_v1.2.0,
> no matter what Ga 3d core electrons treat as valence
> electrons. I am always
> found
> negative frequencies in the output file.
> 
> I guess that I am not the first people to ask why?
> but I don't know how to
> search
> old Pw_forum digest. If someone really know what's
> volume and number have
> talk about negative phonon frequencies, please tell
> me.
> 
> Thank you
> 
> Lu Fu-Fa, 10/02/2003
> 
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum


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