[Pw_forum] keep getting negative frequencies in phonon calculation

[Khalid Ibne Masood Khalid]

Dear Researchers,
I think this is an old problem, but I require your advice about how to
solve this problem. I am trying to calculate the phonon dispersion curve of
a 2D insulator material, and followed example 02 of phonon program. In the
ph.x input file I have used:

  tr2_ph=1.0d-12,
  ldisp=.true.,
  nq1=2, nq2=2, nq3=1

[increasing nq1 and nq2 will be more complicated]

I have tried almost all types of asr, zero-dim, crystal and simple, but yet
I am getting negative frequencies in the phonon dispersion curve.

Now Sir, what should I do to correct this problem. Should ldisp = .false.
solve the problem?

Thank you.

Khalid Ibne Masood
M.Sc student
BUET
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