On Wed, 16 Jul 2008, lfhuang at theory.issp.ac.cn wrote: LFH> Dear all friends:
dear <insert name here>, LFH> I have a question on convergence criterion in supercell, which is: LFH> LFH> For unit cell, I define "conv_thr" and "tr2_ph" to be 1*d-12 and LFH> 1*d-14,respectively. Then I take a 4*4*4 supercell, and is it LFH> precise enough to define 4*4*4*d-12 and 4*4*4d-14 for "conv_thr" LFH> and "tr2_ph" respectively? If it is not, what is the reason? perhaps you should first explain _your_ rationale for lowering the convergence threshold when increasing the system size. a convergence parameter that would depend this much on the system size would not be a good choice. in any case, the rationale to choose a specific convergence criterion should be based on the convergence of the property that you are interested in. i.e. if you want to do a geometry optimization, the forces have to be converged accurately enough, not only with respect to wavefunction/density-cutoffs, k-point sampling but also relative to the wavefunction convergence. similarly, for other calculation types. cheers, axel. LFH> LFH> Thanks a lot for your time to read my letter! LFH> And I would like greatly appreciate the one who can give me some resonable LFH> rationale! LFH> LFH> Best Wishes! LFH> LFH> LFH> _______________________________________________ LFH> Pw_forum mailing list LFH> Pw_forum at pwscf.org LFH> http://www.democritos.it/mailman/listinfo/pw_forum LFH> -- ======================================================================= 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.
