Hello Vincenzo, Thanks a lot for your reply.
"First thing that i would try is to check if phonon calculations at a q point where matdyn gives you negative is correct or not" How would I check this? Also I am using tr2_ph = 1e-18 in the ph.in and conv_thr=1.0d-12 in the pw.in file. My kgrid is 14*12*1 in the pw.in file. Thanks, Ankit Jain On Sun, Aug 31, 2014 at 1:13 PM, Vincenzo Verdolino < vincenzo.verdolino at gmail.com> wrote: > Dear, > > I have similar issues so i am not sure to be able to help you. First thing > that i would try is to check if phonon calculations at a q point where > matdyn gives you negative is correct or not. If yes that means that you > k-samplin is good enough and it is only a matter of q mash for the FFT. > Another check should be on the scf thrashold in ph.in input file > > > Let me know > > Sent from my iPhone > > > On 31/ago/2014, at 17:03, ankit jain <ankitjain.me.iitk at gmail.com> > wrote: > > > > > > Hello QE developers and users, > > > > Recently, I am trying to calculate phonon dispersion of a 2D material > using pw.x, ph.x, q2r.x and matdyn.x but I am getting very strange results. > > > > In my calculations the phonon frequencies reported by ph.x are all real > for all non-gamma phonon q-points. But, when I use matdyn.x to calculate > phonon frequencies at other points (other than the one for which ph.x > calculated frequencies), I get negative (imaginary) frequencies. And these > negative frequencies are present for non-gamma points as can be seen in > attached frequency file. > > > > I am having difficulty in understanding these results and hoping someone > could help. > > > > Thank You, > > Ankit Jain > > PhD Candidate > > IIT India > > > > <pw.in> > > <ph.in> > > <q2r.in> > > <matdyn.in> > > <frequency> > > _______________________________________________ > > 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 > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140831/b4ade94d/attachment.html
