Dear Nicola, thanks a lot, a very interesting read!
Best, Chris On Fri, Sep 7, 2018 at 2:58 PM, Nicola Marzari <[email protected]> wrote: > > > > Hi Christoph, > > > a dual of 2 is cutting a lot of corners for norm-conserving > pseudopotentials (where a dual of 4 is mathematically perfect, > and one of ~3 could actually work). > > Convergence in the total energy for norm-conserving at dual of 4 > is strictly variational, but also not very interesting as a criterion. > > The phonon frequencies are an interesting criterion, but are not > variational. > > So, there is nothing fool proof - but a preponderance of evidence > helps feeling better - this is discussed at length here: > https://arxiv.org/abs/1806.05609 > > > nicola > > > > > On 07/09/2018 10:43, Christoph Wolf wrote: > >> Dear all, >> >> I am afraid that this is a very basic question but I will ask it anyway >> in the hopes of some pointers. I have recently studied the convergence >> behavior of a set (Mg and O) pseudos with respect to the phonon frequencies >> and I encounter a behavior that I quite not understand. >> >> I study the convergence of total energy and the highest phonon frequency >> at q=(0.5,0.5,0.5). I vary the dual=ecutrho/ecutwfc=2,4,8. >> >> for the norm-conserving pseudos (standard dual is 4 here) energy >> converges (monotonously) at a ecutwfc=50 irrespective of the dual. however >> the phonon frequency only converges (strongly non-monotonously, i.e. in a >> zig-zag pattern) if (i) ecutwfc=100 and dual 8 OR (ii)ecutwfc=200 and dual 4 >> >> for the PSLibrary 1.0.0 pseudos the total energy converges (monotonously) >> at ecutwfc=50 for all duals but interestingly so does the phonon frequency >> (in excellent agreement with the converged norm.-cons.!). Varying the dual >> from 2 to 8 leaves the phonon frequencies virtually unchanged. the >> suggested hardest cutoff for the pseudos (from the file) is Mg: 97/398 - >> higher than what I found. >> >> Now I have read that for phonons and US/PAW often a dual of 8-12 is >> advised (I think the example is for metals not an insulator as MgO) but I >> was curious if there is any "fool proof" method to ensure the convergence >> whilst not risking falling in a "local minima" of a phonon frequency, for >> example? >> >> Thanks for reading all the way down to hear, your help is greatly >> appreciated! >> >> Best, >> Chris >> >> -- >> Postdoctoral Researcher >> Center for Quantum Nanoscience, Institute for Basic Science >> Ewha Womans University, Seoul, South Korea >> >> >> _______________________________________________ >> users mailing list >> [email protected] >> 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 > -- Postdoctoral Researcher Center for Quantum Nanoscience, Institute for Basic Science Ewha Womans University, Seoul, South Korea
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