Hi Nic, 1) I have tested the pseudo-potentials (psps) with small atomic separations. The pseudo-potentials give reasonable till two atoms are as close as 0.8 A. When the total energy starts to diverge, which is about Ionic iteration 17, the smallest inter-atomic distance is about 1.4 A. So I do not think the breakdown of the psps is the trigger of this divergence of the total energy, although it should be the reason for the enormous large negative energies.
2) I have tried to restart the calculation from where the divergence starts. Once I did that, the first scf calculation would give a reasonable energy around -41.7 Ry, and the calculation could run smoothly till the total energy converges most of the times. So what I deal with this problem right now is to restart calculations from where they start to have diverged total energies and it's been working well. However, I hope this is not the optimal way to solve this problem. :) Thank you very much, Hui On Thu, Oct 16, 2008 at 3:09 PM, Nicola Marzari <marzari at mit.edu> wrote: > Hui Tang wrote: > > Dear all, > > > > I'm trying to do cell relaxation on my Mg-Boron systems. For some of the > > structures, I got extremely strange results. The total energy diverges > > starting from some ionic step. For example, here are the total energy in > > each ionic step for one of the problematic run: > > > > Two suggestions > > 1) are atoms overlapping much more than they should ? I.e. are these > new configurations reasonable, or are core overlaps very significant ? > The pseudopotential approximation breaks down if cores overlap (a lot). > > 2) is it a bug/memory overrun ? Take the first configuration with > much lower energy, and rerun that from scratch. Do you get an > energy that looks like -41.7 Ry, or much lower ? > > nic > > > > --------------------------------------------------------------------- > Prof Nicola Marzari Department of Materials Science and Engineering > 13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA > tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu > _______________________________________________ > 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/b17a8b89/attachment.htm