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

[Paolo Giannozzi]

On Jul 20, 2012, at 7:56 , Koushik Pal wrote:

> The system is Sb2Se3 (SG-166). No, the scalar relativistic phonon  
> calculation
>  also does not have correct symmetry.

what about the symmetry of the self-consistent calculation? If it is  
not what
you expect, please note the following:

http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/ 
node19.html#SECTION000600190000000000000

> I have one more question. Why doesn't the pw.x code give pressure  
> on the system
> in spin-orbit calculation?

it does: specify tstress=.true. in &control

P.
> ------------------------------
>
> 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
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://www.democritos.it/mailman/listinfo/pw_forum
> --
> 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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---
Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222