[Pw_forum] Fwd: Phonon dispersion from using matdyn.x

[Vincenzo Verdolino]

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