Hi Axel, I have used a much larger cutoff energy to rerun a problematic calculation. This rerun does not have the divergence problem any more. I'm going to do a few more runs to confirm this.
I think it's just as what you said that the effective cutoff energy becomes smaller as the cell expands. So I probably should check the convergence of stresses in my largest cell with respect to the number of plane waves. btw, I did ghost states tests for my pseudo-potentials and there isn't any. p.s., I remember to put on my affiliation this time. :) Thank you very much, --------------------------------------------- Hui Tang Graduate Student Department of Applied Physics Yale University Email: hui.tang at yale.edu Phone: 1-203-432-7763 On Thu, Oct 16, 2008 at 4:00 PM, Axel Kohlmeyer <akohlmey at cmm.chem.upenn.edu > wrote: > On Thu, 16 Oct 2008, Hui Tang wrote: > > hi hui, > > your cell is expanding quite a bit and your cutoff is not > that large. with an expanding cell, your _effective_ cutoff > becomes much smaller as the number of plane waves remains > constant during a variable cell calculation. have you tested > the stess tensor convergence vs. the cutoff? you basically > have to figure out how many plane waves you need for a well > converged stress tensor at the largest expansion of your cell > and then you have to set the cutoff at the beginning so that > it results in the same number of plane waves... > > that would explain why it works (better) if you restart. > > also, did you test the pseudopotentials for ghost states? > > cheers, > axel. > > p.s.: please provide an affiliation. thanks. > > HT> Hi Nic, > HT> > HT> 1) I have tested the pseudo-potentials (psps) with small atomic > HT> separations. The pseudo-potentials give reasonable till two atoms are > as > HT> close as 0.8 A. When the total energy starts to diverge, which is about > HT> Ionic iteration 17, the smallest inter-atomic distance is about 1.4 A. > So I > HT> do not think the breakdown of the psps is the trigger of this > divergence of > HT> the total energy, although it should be the reason for the enormous > large > HT> negative energies. > HT> > HT> 2) I have tried to restart the calculation from where the divergence > starts. > HT> Once I did that, the first scf calculation would give a reasonable > energy > HT> around -41.7 Ry, and the calculation could run smoothly till the total > HT> energy converges most of the times. So what I deal with this problem > right > HT> now is to restart calculations from where they start to have diverged > total > HT> energies and it's been working well. However, I hope this is not the > optimal > HT> way to solve this problem. :) > HT> > HT> Thank you very much, > HT> Hui > HT> > > -- > ======================================================================= > 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. > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20081016/b6730b73/attachment.htm
