[Pw_forum] Imaginary phonon frequency

[Caloma Trumica]

Dear All,

I used nq1 = 4, nq2 = 4, nq3 = 1 to do a phonon calculation. The resulting
inequivalent number of q points is 6.

After a phonon calculation, all frequencies at these 6 points are real and
reasonable.

However, when I used these data to get a full phonon dispersion in the
first BZ. I found that some q points have imaginary frequencies.

Can someone tell me the possible reasons?

Thank you.

Andy
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