[Pw_forum] Phonon Calculation

mayank gupta mayankaditya at gmail.com
Thu Dec 9 05:29:14 CET 2010


I have performed  phonon calculation for silver oxide with mesh size
8x8x8 and ecut off is 70 Ry erhocut=1050 Ry.  I have tested the total
energy convergence. We have used the pseudopotetial generated by using
 PBE . After SCF calculation we performed phonon calculation at
different pressure with 2x2x2 q point using default cutoff parameters
and calculate the gruneisen parameters. The calculated Gruneisen
parameter and thermal expansion are in agreement with our previous
calculation using  potential model lattice dynamics as well as with
experimental results. Again I have performed the same calculation with
4x4x4 q point mesh I find the entirely different result. my main
concern is around q=0 because around that I found the significant
change in phonon frequency. I have used matdyn.x to generate phonon
frequency at intermediate point. Further in acoustic sum rule if I
used asr=simple I am getting the negative frequency while asr=crystal
I didn't get any negative phonon frequency. So I am confused which sum
rule should use and how much q point I have to calculate. Kindly
suggest me .

Thanks  A lot

M K gupta

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