[QE-users] Choosing convergence criteria for vc-relax

[Michal Krompiec]

Dear Nicola,
I am looking forward to reading the "short thing on this"!
Can you comment on the widespread (?) practice of using much lower than
recommended (say, 2/3 or 1/2) ecutwfc for geometry optimization until a
minimum is found, and then increasing cutoffs until convergence is
achieved? Is it generally a good idea?

Best regards,

Michal Krompiec

Associate Director at Merck KGaA and Adjunct Prof at University of
Southampton


On Sun, 19 May 2019 at 13:57, Nicola Marzari <nicola.marzari at epfl.ch> wrote:

>
>
> Hi Robert,
>
> this issue of optimal parameters is a bit of a neverending story, we are
> preparing a short thing on this. But in a nutshell - yes, the electronic
> convergence should be tighter, especially for a follow-up phonon
> calculation. that number actually depends on the unit cell used, but for
> 5 atoms, I would indeed try d-12 and d-14. For ecutwfc and ecutrho,
> well, my advise is to use the SSSP suggestions (google it); and say if
> you have 30 120, 40 160, 25 300, well, take the max of the ecutwfc
> suggested, for the gloval ecutwfc, and same for ecutrho.
>
>                         nic
>
>
> On 17/05/2019 21:24, Appleton, Robert J wrote:
> > Hello,
> >
> > I am trying to study the phonons of the material BaZrS3 to determine if
> > it is stable for a given structure. I first use phonopy and vasp and
> > found negative frequency values for phoning band structure. My advisor
> > is concerned in the optimization of the structure and so we now want to
> > use quantum espresso. I have only used it a few times and mostly used
> > default or example inputs. The input I want to make sure is sufficient
> > is my criteria for convergence.
> >
> > Under the &control:
> > force convergence criteria right now is
> > forc_conv_thr = .0001 <— this value seems to big but how do I choose a
> > value that is best for optimization but does not take to much computer
> time?
> >
> > Under the &electrons:
> > conv_thr = 1.d-9 <— I am considering changing to 1.d-12. Is this a good
> > idea?
> >
> > Under &system:
> > I am using ecutrho = 12 • ecutwfc
> >
> > If you can give me some advice on how best to choose convergence
> > criteria for studying phonons that would be very good thanks.
> >
> > Robert Appleton
> > Cal State LA - MS Physics Student
> >
> > Get Outlook for iOS <https://aka.ms/o0ukef>
> >
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>
>
> --
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
> http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)
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