[Pw_forum] negative phonon frequencies for 1-D polymer chain

[ankit jain]

Hello Andrea,

I am not using 5.0.3 patch to QE 5.0.2 right now and I guess this is the
issue. I will try using it today and will see how things go.

Thanks a lot,
Ankit Jain


On Mon, Apr 14, 2014 at 3:24 AM, Andrea Dal Corso <dalcorso at sissa.it> wrote:

> Did you apply the 5.0.3 patch to QE 5.0.2? Without the patch, the phonon
> code gives wrong frequencies for some q points.
>
> HTH,
>
> Andrea
>
>
> On Mon, 2014-04-14 at 01:19 -0400, ankit jain wrote:
> > Hello Sanjeev,
> >
> > The pseudopotentials I am using are
> > H.pz-vbc.UPF<
> http://www.quantum-espresso.org/wp-content/uploads/upf_files/H.pz-vbc.UPF>
> >  and C.pz-vbc.UPF<
> http://www.quantum-espresso.org/wp-content/uploads/upf_files/C.pz-vbc.UPF>
> >
> >
> > Pseudopotential type: NORMCONS
> > Method: Von Barth-Car (direct fit)
> > Functional type: Perdew-Zunger (LDA) exch-corr
> > scalar relativistic
> >
> >
> > I have tried kgrid of 1*1*6 and 1*1*12, but both give negative
> frequencies.
> >
> >
> >
> > On Mon, Apr 14, 2014 at 12:18 AM, Sanjeev Gupta
> > <physics.skgupta at gmail.com>wrote:
> >
> > > what is kind of pseudopotential?
> > > How much k-point?
> > >
> > >
> > > wishes
> > > sanjeev
> > >
> > >
> > > On Sun, Apr 13, 2014 at 9:25 AM, Ankit <ankitjain.me.iitk at gmail.com
> >wrote:
> > >
> > >> Hello QE developers and users,
> > >>
> > >> I am trying to calculate phonon dispersion using ph.x and matdyn.x
> > >> routines of QE and I am stuck woth negative frequencies for a while
> now.
> > >>
> > >> I have a 1-D chain of polyethylene which has 6 atoms in the unit-cell.
> > >> The polymer chain is aligned in z-direction and I have added vacuum on
> > >> x- and y- direction. I did the structure relaxation and I am getting
> > >> total force after relaxtion as 0.000020, which I guess is sufficiently
> > >> small.
> > >>
> > >> After relaxation, when I am trying to calculate phonon dispersion
> using
> > >> ph.x and matdyn.x I am getting netting frequencies for some of the
> > >> phonon modes. I  searched online and on QE mailing list and tried
> couple
> > >> of different things:
> > >>
> > >> 1. The negative frequencies are appearing for non-gamma point as well,
> > >> so I guess its not a ASR issue. Anyway, I am using ASR but even after
> > >> this I am getting negative frequencies.
> > >> 2. I reduced my tr2_ph and conv_thr to 1.0d-14 and 1.0d-15 which I
> guess
> > >> are very small as suggested on QE FAQs.
> > >> 3. I checked phonon mode shapes for modes with negative frequencies
> and
> > >> they do not look like rotational mode.
> > >> 4. I tried changing number of k points from 6 to 12 in z direction but
> > >> this is also not the cause.
> > >>
> > >> I am really stuck here and not sure about the cause of negative
> > >> frequencies. With vc-relax, my structure is getting relaxed which I
> > >> guess means my structure is stable. But then I am not sure why I am
> > >> getting negative frequencies.
> > >>
> > >> I really appreciate any help or suggestions.
> > >>
> > >> Thanks,
> > >>
> > >> Ankit Jain
> > >> IIT Indore,
> > >> Indore,
> > >> India
> > >>
> > >>
> > >> _______________________________________________
> > >> Pw_forum mailing list
> > >> Pw_forum at pwscf.org
> > >> http://pwscf.org/mailman/listinfo/pw_forum
> > >>
> > >
> > >
> > >
> > > --
> > > With Best Regards,
> > >
> > > ------------------------------------
> > > Dr. Sanjeev Kumar Gupta
> > > Fulbright Post-Doctoral Scholar
> > > Dept. of Physics
> > > Michigan Technological University
> > > 1400 Townsend Drive, Houghton
> > > MI 49931, USA
> > > ------------------------------------
> > >
> > > _______________________________________________
> > > Pw_forum mailing list
> > > Pw_forum at pwscf.org
> > > http://pwscf.org/mailman/listinfo/pw_forum
> > >
> > _______________________________________________
> > Pw_forum mailing list
> > Pw_forum at pwscf.org
> > http://pwscf.org/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
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140414/78d9f1e6/attachment.html>