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