[QE-users] Acuostic Sum Rule:-Regarding

[Suresh A]

Dear All,
             I am asking this question to know whether I have made a
mistake in my calculations during my run using phonon code in pwscf. I also
went through previous posts but could not understand as I am not good at
phonon theory.
I have run calculations for three alloys. Two of them give positive
frequencies for  zasr='crystal' as well as for zasr='simple' but for one
alloy it gives negative frequency for zasr='simple' and positive frequency
for zasr='crystal'. Due to curiosity I just simply increased the
convergence threshold for phonon calculation alone (not in any other part
in scf) from  tr2_ph = 1.0d-12, to tr2_ph = 1.0d-14, Now the results are
reversed. I got positive frequency for zasr='crystal' and negative
frequency for zasr='simple. I want to ask two questions from this,

1. May I claim my alloy is a stable one, because the previous report says
that it is an unstable structure?
2.I want to know whether I have made any mistake in my run?
Following is my procedure I used for my calculations:
1. SCF
2. Phonon run
3. q2r with zasr = simple and zasr= crystal
4. PlotPhon code for postprocessing (I have run for other two alloys for
which there is no negative frequency for zasr= simple and crystal.) Here I
simply used this code immediately after  I ran q2r by simply changing
asr='crystal' to simple  in the folder PlotPhon-> Scripts-> Plot_run.
Did i make any mistake here?

Thanks and regards

                 Yours Sincerely,

 A.Suresh,
Post-Doctoral Fellow
Department of Physics
National Institute of Technology
Tiruchirappalli
Tamil Nadu,
India
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