[QE-users] Doubt regarding the phonon calculations of RbPbI3

[Lorenzo Paulatto]

Try to reduce conv_thr to 1.d-12 and tr2_ph to 1.d-18. The cutoffs are pseudopotential dependent, I cannot comment on them. Yet, the most likely source of error is that you have used the an incorrect cell parameters and/or atomic coordinates.

kind regards
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
http://www.impmc.upmc.fr/~paulatto/ (https://link.getmailspring.com/link/0DB23530-E66D-4007-A884-42766DAFC06F@getmailspring.com/0?redirect=http%3A%2F%2Fwww.impmc.upmc.fr%2F~paulatto%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D) - https://anharmonic.github.io/ (https://link.getmailspring.com/link/0DB23530-E66D-4007-A884-42766DAFC06F@getmailspring.com/1?redirect=https%3A%2F%2Fanharmonic.github.io%2F&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D)
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On Sep 22 2021, at 3:43 pm, Anupriya Nyayban <mamaniphy at gmail.com> wrote:
> I have calculated the phonon dispersion of orthorhombic RbPbI3 (Pnma) using "PHONON" as implemented in Quantum Espresso and found the negative frequencies ( which should not be present as suggested in https://doi.org/10.1063/1.5131575 (https://link.getmailspring.com/link/0DB23530-E66D-4007-A884-42766DAFC06F@getmailspring.com/2?redirect=https%3A%2F%2Fdoi.org%2F10.1063%2F1.5131575&recipient=dXNlcnNAbGlzdHMucXVhbnR1bS1lc3ByZXNzby5vcmc%3D)). It would be great help if you suggest to me where I am doing wrong!!! I have provided the computational details below:
> 1) The structure first is being relaxed and then the convergence tests are performed for Ecut, Kmesh and Lattice parameters.
> 2) Using the relaxed structure with converged parameters, SCF is performed with cov_thr=1.0d-8 (ecutwfc=70, ecutrho=600, kmesh=12*6*3); phonon calculation is performed with tr2_ph=1.0d-14 at Gamma point, frequencies are obtained by imposing acoustic sum rule at the Gamma point with asr=simple.
>
> Thank you!!
>
> --
> With regards
> Anupriya Nyayban
> Ph.D. Scholar
> Department of Physics
> NIT Silchar
>
>
>
>
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