Dear Amin: On Sat, May 28, 2011 at 2:26 AM, Amin Torabi <amin.torabi at gmail.com> wrote:
> Dear all, > > I did a vc-relax calculation. Then, I used the cell_parameters and > atomic_positions obtained at the end of vc-relax to do an scf calculation. I > didn't change any other settings, like k-point or ecutoff. > However, the total energy, the total force and the total stress obtained > from the scf calculation are different form the values obtained at the end > of the vc-relax calculation. (The vc-relax values are lower.) > Why is it so? > You are right. When you do vc-relax, the G points contained in wave-function does not change with the cell parameters(That means the energy cutoff changes when cell parameters change during vc-relax). When you do scf after vc-relax, the cell parameters of scf is different from that of vc-relax. Therefore, the G points contained in wave-function of scf differs from that of vc-relax. Usually, you should do the second vc-relax if the cell parameters change a lot. After the second vc-relax, the force/stress of scf will be close to that of second vc-relax. > > > Thanks is advance. > > Amin > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -- ____________________________________ Hui Wang School of physics, Fudan University, Shanghai, China -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110528/a882f756/attachment.htm
