Dear all,
With tr2_ph=1.0d-12 and q-points 2X2X2, there is no imaginary frequency
among the calculated q points, and the frequency of GAMMA point is about 36
cm-1. After dynamic matrix calculation with asr='crystal' and 100
interpolated points, I obtained good phonon spectrum, but if I interpolated
200 points, a small imaginary frequency near GAMMA point appeared.
Then I reduced tr2_ph to 1.0d-14, unfortunately, the frequency of GAMMA
point is about -6 cm-1, but after dynamic matix calculation with asr='crystal'
and 1000 interpolated points, it vanished and there is no imaginary
frequencies at other points. However, 2000 interpolated points in dynamic
matrix calculation courted imaginary frequency near GAMMA point again!
I hope someone can help me with this promblem.
Thank you very much!
Tan Lin
2015.10.29_______________________________________________
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