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

ankit jain ankitjain.me.iitk at gmail.com
Sun Aug 31 17:03:29 CEST 2014


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
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