On Sun, 2014-11-09 at 20:31 +0100, simone marocchi wrote: > Unfortunately the symmetry operations implemented so far in Quantum > Espresso can not handle screw rotations and glide reflections as in a > standard Quantum Chemistry package
? QE should work with all point symmetries that are compatible with translational symmetry P. > . So I am trying to impose such occupations as an approximation to the > real symmetry of the system. Hereafter I will try also your "dirty > trick" suggesting a starting_ns_eigenvalue bigger than one. Using the > mixing_fixed_ns > electron_maxstep I obtained big differences in the > occupations imposed and obtained, interestingly although I did not end > in the predetermined states the system fell always in the same > strange occupation. The convergence was quite nice (tens of > iterations) up to 10^-6 Ry. Perhaps, as you pointed out I have a > different symmetry than the code finds for my system. Unfortunately, > although I would like to try to develop some new parts codes, I do not > feel enough trained and comfortable with the timetable of my current > project. Thanks a lot for your suggestion ! > > > S > > > Dear Simone > > I try to answer your questions below. > > On Fri, Nov 7, 2014 at 3:32 PM, simone marocchi <[email protected]> > wrote: > > > Dear all, I am simulating compounds with rare earths within a > collinear > > calculation. I tried to suggest some occupations of the f orbitals > for the > > Tb atom, using the starting_ns_eigenvalue(m,ispin,I). > > > > > why do you need to do that? if you want to force different values of > occupation on states that are equivalent by symmetry you will not be > successful. If this is the case you have to do something that makes > the > system loose that symmetry operation connecting the two states. > > > > > Unfortunately also with a small value of electronic mixing and big > values > > of U, the imposed occupations was lost during the iterative cycle. > > > > > this can happen. a dirty trick I learned recently is to suggest a > starting_ns_eigenvalue(m, > ispin,I) bigger than one in input (1.2 or 1.3 maybe). This does not > make > any physical sense of course. However the Hubbard potential becomes > more > attractive for the specific eigenvector of the occupation matrix you > want > to fill completely and the code takes more time to "come back" to a > physical value. If that is a state it likes (at least a local minimum > of > the energy) it might fall into it. Of course you have to check at the > end > that the occupation has gone back to a value <= 1. > > > > > So I used also mixing_fixed_ns > electron_maxstep. Also in this case > after > > I obtain the total energy convergence the density matrix of the last > > iteration is different to the one imposed in the input_file. > > > > > this is (possibly) strange. How different is it? How well are you > converging? > The fact that it is different is not surprising: the routine that > prints > the ns, always prints the ones that are computed from the KS states > just > obtained from the new diagonalization. These can be different from the > ones > e.g. used in contructing the Hubbard potential. > However if your calculation is well converged this difference should > not be > big: both KS wfcs and their occupations should be converged reasonably > well. > If this does not happen and you still see a significant difference > maybe it > means that the values you are trying to impose is not consistent with > what > the system wants to do (e.g., you have less symmetry than the code > finds > for your crystal) > > > > > > Can someone of you kindly explain me how the mixing_fixed_ns works ? > Do it > > uses a sort of Lagrange multipliers to force the occupations or is > more > > like a penalty function ? Finally, is it possible to work around the > > problem, converging to a determined occupation ? > > > > > no with the current version of the code. you could implement some > (e.g., > quadratic) constraint and try. I think I once tried (long time ago) > and > seem to remember problems in convergence. > > Best, > > Matteo > > > > -- > Simone Marocchi > > S3 Center, Istituto Nanoscienze, CNR > via Campi 213/A, 41125, Modena, Italy > Tel: +39 0592055585; Skype: jacobi84 > URL: http://www.nano.cnr.it > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
