Hi Paolo, Thanks for your reply. For the phonon calculation, I use a PBE-US PP (Fe.pbe-sp-van_ak.UPF, and Se.pbe-van.UPF). According to your suggestion, I increase the ecutwfc, and do several tests. Unfortunately, it seems there are still convergence problem:
ecutwfc ecutrho f1(cm-1) ... f12(cm-1) 100 1200 106.5 ... 329.5 100 2400 127.2 ... 339.8 200 2400 127.8 ... 341.2 200 4800 32.9 ... 319.8 Could there be any other reasons to cause this convergence problem? Yuyang at RPI On Mon, Apr 16, 2012 at 11:52 AM, Paolo Giannozzi <giannozz at democritos.it> wrote: > On Thu, 2012-04-12 at 16:07 -0400, YY wrote: > >> But I find there is no simple convergence trend while increasing >> ecutrho. ?When I use 35 Ry ecutwfc, and fix all the other parameters, >> the results are like this: >> >> ? ?ecutrho ? ? ? f1(cm-1) ? ? ?.... ?f12(cm-1) >> ? ?420 ? ? ? ? ? ?40.475 ? ? ? ? ? ? ? ?324.062 >> ? ?600 ? ? ? ? ? 123.746 ? ? ? ? ? ? ? 350.727 >> ? ?900 ? ? ? ? ? -251.876 ? ? ? ? ? ? ?306.721 > > unfortunately in at least some [ and I am afraid, in many ] cases, > a rather high cutoff is needed anyway to get decent phonons. If > this happens, the advantage of using USPP becomes dubious, given > their significant computational overhead wrt Norm-Conserving PPs. > Which USPP did you use ? > > P. > > -- > Paolo Giannozzi, IOM-Democritos and University of Udine, Italy > >
