Replying to message "[Pw_forum] graphene on BN calculation" from mohamed sabri majdoub (16/12/09):
> I am not sure that I am doing it the right way. I am using 40 processors > and I the calculations look very slow to me. Well, it's a big system. You can speed it up by using tqr=.true. (real-space augmentation charge). There is also an experimental real-space algorithm, but I don't know how reliable it is at the moment (you can contact baris _at_ sissa.it for additional info). > tstress = .t. there is no need to print the stress, and it takes time to compute (not much) > diagonalization = 'cg' For better performance you should use the default (david). If you have some problem with it, you should ask for help on the forum before falling back to cg, which is non much more robust and quite a bit slower. Also, diagonalization errors are most of the time input errors/bad atomic positions. > K_POINTS automatic > 30 30 1 1 1 0 this is a huge number of k-points for such a cell, are you sure you need all of them? Remember that every time you increase the cell size by N you can reduce the number of k-points by the same factor. (e.g. a 2x2x2 super-cell only need on eighth of the k-points of the original cell). Computation time scales linearly with the number of points, e.g. "10 10 1 1 1 0" will be about 9 times faster. best regards -- Lorenzo Paulatto SISSA & DEMOCRITOS (Trieste) phone: +39 040 3787 511 skype: paulatz www: http://people.sissa.it/~paulatto/ *** save italian brains *** http://saveitalianbrains.wordpress.com/
