[Pw_forum] "Raman activities" do not converge

[Lorenzo Paulatto]

On 05/30/2013 05:29 PM, xirainbow wrote:
>             I  changes the pseudopotential from "C.pw-mt_fhi.UPF" to
> "C.pz-hgh.UPF" and get the expected "Raman activity" for different
> ecutwfc. However, the results of "ecutwfc=110" are still higher than
> others.
>
Compare the output of pw.x at different cutoffs to be sure, my bet is 
that at that specific value of ecutwfc some symmetry operations are 
incompatibles with the FFT grid. It can make convergence harder. In 
general, I found that when you have problems converging response 
(phonon, epsilon, raman...) calculations it's better to use a much 
stricter conv_thr (i.e. 1.d-12). Sometimes I even reduce the hard-coded 
threshold (ethr) in PHonon/PH/set_defaults_pw.f90

bests


-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
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