Dear Hao,
> The kpoint grid I chose is 60*60*60. I suppose you vast time with such kind incredibly large k-mesh. Try increasing nq's for phonon calculations (ph.in). Play around cutoff energy and the threshold parameter for phonons. What is the accuracy of your q2r.x (FFT) run? Bests, Eyvaz. ------------------------------------------------------------------- Prof. Eyvaz Isaev, Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Sweden Theoretical Physics Department, Moscow State Institute of Steel & Alloys, Russia, isaev at ifm.liu.se, eyvaz_isaev at yahoo.com ________________________________ From: HaoPan <[email protected]> To: pw_forum at pwscf.org Sent: Thu, July 29, 2010 9:49:32 PM Subject: [Pw_forum] Fourier interpolation Dear Baroni, The kpoint grid I chose is 60*60*60. nk1=60, nk2=60, nk3=60, I think that is fine enough. Because the q point grid is just 6*6*6. For metal, the frequencies of the gamma point are alway not zero (some small negative value) . Some may cause the frequencies around the gamma point negative. But even all q points I got are positive, there exit negative frequencies after the matdyn.x calculation. I don't know why. Sincerely, Pan Hao Tulane University the kpoint grid you are using may be too coarse dynamical matrices in metals are indeed smooth functions of k, unless you have Kohn anomalies SB On Jul 28, 2010, at 5:33 PM, HaoPan wrote: > Hi, everyone, > > On each q point I got, the phone frequencies are positive. But after the >Fourier interpolation process, There > exist negative frequencies. I check the some special q points using ph.x, > there >are no negative frequencies. I > know the dynamical matrices for metal are not smooth function of q, but how > do >I fix it to get the right > dispersion curves? Thanks a lot. > > Sincerely, > Pan Hao > Tulane University _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100729/68ff7557/attachment.htm
