[Pw_forum] problem in phonon calculation of Na2S

[Stefano de Gironcoli]

premlata pandit wrote:
> Hi users,
> I had some problem in Na2S phonon calculation....
> The Acoustic modes are comming somewhat unrelevent. I feel there are 
> some unusual cross-over also.
sorry I  don't  understand what you mean by unrelevant ...
the plotting tool is just plotting the phonon bands in order of 
increasing frequency, there is  no symmetry analysis so you do not get 
any level crossing (by definition). If you want a nicer picture use a 
denser grid .
Pay attention to the LO-TO splitting... look for variable epsil in the 
ph.x input.
 
hope this helps,

 Stefano de Gironcoli - SISSA and DEMOCRITOS

> If anybody just have a look into the graph and comment on it, whether 
> it is correct or not? I am also sending the na2s.ph.in 
> <http://na2s.ph.in/> and na2s.q2r.in <http://na2s.q2r.in/> file.... Is 
> there any other parameters, I have to consider for calculation of 
> phonon for semiconductors like Na2S??
>        
>
>  Thank you
>
> -- 
> Premlata Pandit
> Ph.d. student,
> Barkatullah university,
> Bhopal 462026,
> MP, India
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