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

[Koushik Pal]

Dear sir,
The system is Sb2Se3 (SG-166). No, the scalar relativistic phonon
calculation  also does not have correct symmetry. I used PBE-GGA NC  PP .
I have one more question. Why doesn't the pw.x code give pressure on the
system in spin-orbit calculation? Can we get any idea of the actual
pressure of the system from the scalar relativistic/non relativistic
calculation?

On Tue, Jul 17, 2012 at 7:24 PM, <pw_forum-request at pwscf.org> wrote:
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Message: 7
Date: Tue, 17 Jul 2012 15:54:12 +0200
From: Andrea Dal Corso <dalcorso at sissa.it>
Subject: Re: [Pw_forum] anomaly in phonon frequencies as obtained
        using   DFPT    (ph.x) in a spin-orbit calculation
To: PWSCF Forum <pw_forum at pwscf.org>
Message-ID: <1342533252.4490.15.camel at ulisse.cm.sissa.it>
Content-Type: text/plain

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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> Andrea Dal Corso                    Tel. 0039-040-3787428
> SISSA, Via Bonomea 265              Fax. 0039-040-3787249
> I-34136 Trieste (Italy)             e-mail: dalcorso at sissa.it
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