[QE-users] -help

[Kiran Yadav]

Hi,
I am trying to calculate full phonon dispersion with born effective charge.
My ph.in file is --
Phonon Calcs for S1
&inputph
 prefix='S1'
  epsil=.true.
  ldisp=.true.
  verbosity='high'
  outdir='./home',
  fildyn='S1.888.dyn'
  nq1=8
  nq2=8
  nq3=8
/

When I use nq1,nq2,nq3 =4 , it generates 20 dynamical matrix file (.dyn),
with nq1,nq2,nq3=8 it generates 35 files and so on with higher nq values..
Each .dyn file takes ~4 hrs on  100 core processor.

My question is  --
1. Is there any procedure to know about nq values which will be okay to get
a phonon dispersion with reliable accuracy.
2. Is there anything similar thing to do like we do a k-mesh convergence
test for scf calculation in order to get a reliable electronic band
structure.
3. Is nq and nk grid similar ?

I tried to give all the information I could, I m new to QE so can't explain
my doubts better than this, so, please update whatever possible.

Thanks in advance

Best,
Kiran

On Tue, Nov 3, 2020, 18:22 Lorenzo Paulatto <paulatz at gmail.com> wrote:

> > Is there any methodology to check and decide nq-grid points for phonon
> > dispersion spectra calculations?
>
> I'm not sure what calculation you are trying to do.
> Can you provide a more detailed description?
>
> Do not forget the second law of question-answer conservation:
> «In a not-being-paid-for frame of reference,
> the amount of time spent answering a question
> will never exceed the amount of time spent asking it»
>
>
>
> --
> Lorenzo Paulatto - Paris
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