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 > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140414/e244fc34/attachment.html
