On Sat, 10 May 2008, Roberto G. A. Veiga wrote: RV> Dear Stefano: RV>
RV> I'm using Ultrasoft PPs. My question was because this cutoff (20 Ry) RV> seemed to be appropriate for other carbonic systems. dear roberto, as stefano mentioned, what is appropriate depends on the individual potential(s) and the properties that you are iterested in. while 20-30ry is the usual wfc range for uspps, they also tend to require a higher density cutoff than the default 1:4 ratio that is adequate for norm-conserving pseudopotentials. there is no "automatically good" values and a "good beyond any doubt" setting is usually a huge waste of cpu time. there have been attempts to encode cutoff requirements into pseudopotential files to make this whole process a little bit less of a guesswork for unexperienced users, but for the reasons outlined above, it is very difficult to make a choice. it is one of the items, where you just have to know what you are doing and run the required tests by yourself... :-( cheers, axel. RV> RV> []s, RV> RV> Roberto RV> RV> Stefano Baroni <baroni at sissa.it> wrote: RV> On May 9, 2008, at 10:42 PM, Roberto G. A. Veiga wrote: RV> RV> Hi, Konstantin: RV> RV> thank you very much. Such a large cutoff (80 Ry) is necessary for convergence? Or maybe I'm using one quite small (20 Ry)... RV> RV> it depends on the PP you are using, I guess, and certainly NOT on the actual structure you are studying. 80 Ry seems like an appropriate cutoff for moderately hard norm-conserving PP's, whereas 20 Ry sounds like appriate for many US PP's. In either case, you better check the aprporiateness by yourself, through thorough convergence tests. RV> RV> RV> Stefano RV> RV> RV> RV> RV> RV> []s, RV> RV> Roberto RV> RV> Konstantin Kudin <konstantin_kudin at yahoo.com> wrote: Hi Roberto, RV> RV> Here is a ribbon input that works for sure: RV> https://kiev.princeton.edu/misc/rg_07.scf.in RV> (get PPs from the PWSCF website) RV> RV> Good luck! RV> Kostya RV> --- RV> Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste RV> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) RV> RV> RV> La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget RV> RV> RV> RV> Please, if possible, don't send me MS Word or PowerPoint attachments RV> Why? See: http://www.gnu.org/philosophy/no-word-attachments.html RV> RV> RV> RV> RV> RV> RV> RV> RV> RV> RV> RV> _______________________________________________ RV> Pw_forum mailing list RV> Pw_forum at pwscf.org RV> http://www.democritos.it/mailman/listinfo/pw_forum RV> RV> RV> RV> --------------------------------- RV> Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. -- ======================================================================= Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu http://www.cmm.upenn.edu Center for Molecular Modeling -- University of Pennsylvania Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323 tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425 ======================================================================= If you make something idiot-proof, the universe creates a better idiot.
