I am confused: no electric field, no Berry phase - what I suggested you to try is whether the stress calculated from finite differences and from the Hellmann-Feynman theorem give the same result (no Berry phase in either case). I am confident they do. SB
On Apr 2, 2009, at 7:12 AM, hanghui chen wrote: > Yes. At vanish electric field, even with USPP the stress is the same > as the normal calculation (without using Berry Phase method). > Hope this helps. > > Is your calculated stress OK with USPP at vaishing electric field? > SB > > On Apr 1, 2009, at 4:48 PM, hanghui chen wrote: > > > Dear PWscf developers and in particular Professor Baroni, > > Thank you very much for your instructions. > > I did the test to check the forces and stress in the Berry > > phase method with the ultrasoft pseudopotential. The forces are > > correct but the stress is around 50% smaller. I am not sure whether > > it is due to the ultrasoft pseudopotential or not. > > I would greatly appreciate it if the developers of QE could > > reexamine the calculation of stress in the Berry phase method with > > the ultrasoft pseudopotential. > > Best wishes. > > > > Hanghui Chen > > Department of Physics, > > Yale University > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum --- Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype) La morale est une logique de l'action comme la logique est une morale de la pens?e - Jean Piaget Please, if possible, don't send me MS Word or PowerPoint attachments Why? See: http://www.gnu.org/philosophy/no-word-attachments.html -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090402/d783182b/attachment.htm
