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
