[Pw_forum] non degenerate phonon frequency for cubic crystal along 1 0 0
Stefano de Gironcoli
degironc at sissa.it
Fri May 13 08:43:39 CEST 2011
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 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)
> 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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