Thanks Stefano, Nicola, I already use the no_sym flag, which prevents the charge density from being symmetrized with respect to all symmetry operations. However, even with the no_sym flag, only half the k-points are generated (e.g. for a 4x4x4 mesh the code generates 32 points and all the ones with negative k_x are missing). Here Stefano's idea of supplying a k-point list myself, would help. But, it is not that simple, is it? If inversion symmetry and time reversal are present, the wave functions can be chosen real (by real I mean that the wave functions only have a constant arbitrary phase factor). So, if I break time reversal and give the code my own, complete k-point list, does the code anywhere still assume that the wave functions are "real"? Maybe breaking inversion symmetry by hand could help?
Timo Nicola Marzari wrote: > Stefano Baroni wrote: > >> Timo: I do not have a solution handy, and others may have deeper ideas. >> I think the problem is that when simmetrizing the charge density the >> code always assumes e(k)=e(-k) and psi(-k)=psi(k)*, and so it never uses >> more than 1/2 the BZ. One thing you may try is to pass explicitly all >> the k-points, and wish that the code is not so smart as to remove 1/2 of >> them ... Otherwise, I do not see any other options than hacking the code >> (but, again, others may have smarter ideas). SB >> > > Timo - what about the no_sym flag ? I thought that that would allow > to force pwscf not to try to symmetrize the points (e.g. if > one wanted to use a Baldereschi point, such as 1/4 1/4 1/4) - since > it does not attempt to symmetrize anything, it might not use > time reversal (rambling hypothesis - I'm sure SdG or PG know better, > as always the case :-) ). > > As a side note - once k and -k are treated separately, even > if the Hamiltonian is invariant for time reversal, > in principle it's not psi(-k)=psi(k)* , but you might > find more generally that psi(-k) = exp (i alpha) psi(k)* , > where alpha is random. > > > nicola > > > --------------------------------------------------------------------- > Prof Nicola Marzari Department of Materials Science and Engineering > 13-5066 MIT 77 Massachusetts Avenue Cambridge MA 02139-4307 USA > tel 617.4522758 fax 2586534 marzari at mit.edu http://quasiamore.mit.edu > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- ______________________________________________________________________ Dr. TIMO THONHAUSER Department of Materials Science and Engineering (617) 253 6026 MIT, 13-4084, 77 Massachusetts Avenue thonhauser at mit.edu Cambridge, MA 02139-4307, USA www.mit.edu/~thonhaus ______________________________________________________________________
