[Pw_forum] anomaly in phonon frequencies as obtained using DFPT (ph.x) in a spin-orbit calculation

[Andrea Dal Corso]

Can you give more information? Which system is it? Does the scalar
relativistic phonon calculation have the correct symmetry?

A.

On Tue, 2012-07-17 at 18:46 +0530, Koushik Pal wrote:
> Dear sir,
>   I calculated the phonon frequencies of a system using both the
> frozen phonon method as well as DFPT (ph.x) in fully relativistic
> regime (spin-orbit interaction) using QE verson 4.3. According to
> group theory the 12 optical modes of the system are 2A1g + 2Eg + 2A2u
> +2Eu. I got accurate results for the frequncies in the frozen phonon
> method (means, the frequencies obeyed the symmetry rule as predicted
> by the group theory. Also I visualized the eigenmodes which also agree
> well), but in the DFPT (linear response theory), the obtained
> frequencies and eigenmodes do not obey the above symmetry principles
> as predicted by group theory (though the frequencies are near the
> frequencies as obtained in frozen-phonon method) . It seems that the
> degeneracies in the frequencies are broken in DFPT. What is the reason
> behind that? Please help. Please give references with mathematical
> details (if available).
> 
> Thanks in advance.
> 
> =============
> Koushik
> Grad. student
> Chemistry and Physics of Materials Unit
> JNCASR
> Bangalore , India
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