[Pw_forum] non degenerate phonon frequency for cubic crystal along 1 0 0

[Stefano de Gironcoli]

Does the scf calculation find the expected symmetry ?  then I'm 
surprised that the dynamical matrix does not show it.
Does the structure look as it should when visualized with xcrysden ?
Are you providing the atomic coordinates with enough digits ?

stefano
-
Stefano de Gironcoli - SISSA and DEMOCRITOS

On 05/12/2011 10:38 PM, Paolo Giannozzi wrote:
> On May 12, 2011, at 17:43 , mayank gupta wrote:
>
>> The phonon frequency for cubic crystal should have degenerate
>> along [1 0 0] for TA modes, But i got different frequency. I have
>> calculate  the same with larger value of ecut_rho as well as with
>> higher FFT mesh and still they are non degenerate.
> symmetry doesn't change with the cutoff. You may want to try
> a tighter convergence criterion (tr2_ph)
>
> P.
> ---
> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
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