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> 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 > ) > > users mailing list 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) > users mailing list users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users >
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