[QE-users] Full phonon dispersion calculation not converging for 2d monolayer

[Giovanni Cantele]

Hi,
I'm not very expert about phonon calculations. There is no indication of
the atomic species in your files. However, you should try to visualize your
structure, to understand if it looks exactly as you expect. I tried it, and
obtained what you see in the attached figure.

Moreover, you should also check your ground state calculation, to
understand whether or not it has converged. Indeed, if you look at lines
like these ones
pert. #  1: Fermi energy shift (Ry) =     3.7082E+22    -1.2500E-01

      iter # 100 total cpu time : 78743.4 secs   av.it.: 167.3
      thresh= 1.000E-02 alpha_mix =  0.700 |ddv_scf|^2 =  3.427E+47

I would say that figures like 3.7082E+22 or 3.427E+47 do not look so
reasonable.

As for the scf calculation, where reducing mixing_beta might help in some
cases to overcome problems related with the convergence of the scf cycle,
you might try to reduce alpha_mix =  0.700. However, given the
unreasonables values printed in your output (see above), I would not be so
confident that this would solve your problem.

So, try to check all the steps of your calculation, starting from the
geometry optimization.

Giovanni


[image: image.png]
-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: https://sites.google.com/view/giovanni-cantele/home


Il giorno lun 13 feb 2023 alle ore 14:52 sunilch.cstaff via users <
users at lists.quantum-espresso.org> ha scritto:

> Dear QE community,
>
> I am trying to converge a full phonon dispersion calculation for a
> monolayer material. However, the calculation is not converging for
> convergence thresholds less than 10^-12. I have tried changing the
> alpha_mix from 0.9 to 0.1 but still, the problem remains. I also tried
> increasing the vacuum size in the z-direction from 10 A to 20 A but
> still, the problem persists. There is a pattern that the convergence
> decreases until 10^-12 and then starts to shoot up to large values (for
> eg. upto 10^10). I am using full relativistic ultrasoft pseudopotential
> with PBESOL functional.
>
> I need help with why this is happening and how it can be resolved.
>
> I am attaching the scf and phonon calculation files.
>
> The convergence starts to shoot up after iteration 18.
>
> --
> Regards,
> Sunil Choudhary
> Junior Research Fellow
> DMSE, IIT Delhi
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