Dear Nicola, Thank you very much! Regards, Michal On Mon, 20 May 2019 at 20:04, Nicola Marzari <nicola.marz...@epfl.ch> wrote:
> > > Dear Michal, > > > it depends on how smooth is the dependences of the forces on the cutoff, > so one should make an informed decision depending on the > pseudopotentials used. We e.g. look at phonon frequencies as a function > of cutoff, and if you look at silicon, here below, even if we didn't > test below 30Ry, I would bet that at 20 or even 15Ry forces would be > reasonable: > > > https://www.materialscloud.org/discover/data/discover/sssp/convergences_efficiency/Si_8.0_conv_patt.png > > If you try Ga, you can see that the phonons (the solid line) do not > particularly become worse in going down from 70Ry to 45Ry, but then > progressively worsen: > > > https://www.materialscloud.org/discover/data/discover/sssp/convergences_efficiency/Ga_8.0_conv_patt.png > > Still, for many pseudopotentials a decrease in cutoff doesn't worsen the > forces particularly, but there is no 2/3 or 1/2 rule - one just need to > examine the tables above. > > For ecutrho it might be a bit easier, and if you are not having > magnetism often one can use a dual (the ration of ecutrho/ecutwfc) > equalt to 3, or even 2, for normconserving, and 6 or even 4 for ultrasoft. > > All to be tested... > > nicola > > > On 20/05/2019 13:47, Michal Krompiec wrote: > > 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.marz...@epfl.ch > > <mailto:nicola.marz...@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> > > > > > > _______________________________________________ > > > Quantum ESPRESSO is supported by MaX > > (www.max-centre.eu/quantum-espresso > > <http://www.max-centre.eu/quantum-espresso>) > > > users mailing list users@lists.quantum-espresso.org > > <mailto:users@lists.quantum-espresso.org> > > > https://lists.quantum-espresso.org/mailman/listinfo/users > > > > > > > > > -- > > > ---------------------------------------------------------------------- > > 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 > > <http://www.max-centre.eu/quantum-espresso>) > > users mailing list users@lists.quantum-espresso.org > > <mailto:users@lists.quantum-espresso.org> > > https://lists.quantum-espresso.org/mailman/listinfo/users > > > > > -- > ---------------------------------------------------------------------- > 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 >
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