Dear Maxim, Another point, you set MaxSCFIterations 0 I am not sure but I think this means that you just get your DM interpolated at the new k-points. If you would let the scf-loop reach convergence for the new k-point set I would guess you get more reasonable forces.
Regards Henrik 2011/10/22 Marcos Veríssimo Alves <[email protected]> > Maxim, > > I believe Chun has a point here, and I beg to differ from what you say. > > For some materials, it is important to include special k-points, so as to > get a correct band structure and (eventually) forces - the most "famous" > case would perhaps be graphene, with its K point. Even if your material > hasn't such special characteristics, making the k-point mesh denser means > that you are sampling the BZ more accurately and thus changing the part of > the total energy that corresponds to the electronic band occupations. Just > think of a simple numerical integration in 1-D. > > To say that you have a problem with an increasing k-point mesh density is a > bit precipitated, unless you are sure that you have a very converged k-mesh. > Chun's e-mail is actually very sensible: you should first relax your > structure, and then increase the k-mesh to see its effects on the forces.Not > only that, you should also check its effects on the band structure, although > in principle this effect should be negligible, if you have performed a > convergence study. > > Marcos > > > On Sat, Oct 22, 2011 at 6:34 AM, Maxim Peskov <[email protected]> wrote: > >> Thanks for the comment, Chun. However, you have missed the point. >> I guess it will be better if I rephrase my question: how can one restart >> from scf-preconverged density matrix and increased kpoint set? With the >> options I used such a restart would mean the forces are going crazy which >> clearly indicate a problem. Even more, if I change kpoints it is better to >> start from scratch than to use DM. Any ideas? >> >> --Max >> >> >> 20 октября 2011, 20:04 от [email protected]: >> > Hi, >> > >> > From the first ourput file, I found the following lines: >> > >> > outcoor: Final (unrelaxed) atomic coordinates (fractional): >> > -0.00005348 0.49985936 0.49676159 1 1 C >> > ... >> > ... >> > >> > which means your first run is not converged. >> > >> > Best, >> > >> > Chun >> > >> > >
