On Wednesday, January 13, 2016 07:05:22 PM Francesco Macheda wrote: > Dear all, > I'm new to Quantum Espresso. I'm trying to get the energy bands from > Silicon bulk with hybrid functionals. I've read in previous posts and in > quantum documentation that "Their value (of the q-points) must be > compatible with the k-points used (that is k+q must be equivalent to some > other k in the k-points list)". I'm not certain to understand why it has to > be done this way.
The "correct" way to do EXX is that the q grid is identical to the k grid, in this case every k+q point is equal to another k' point eventually plus a G vector of the reciprocal lattice. Often a reduced grid of q points can be used, but in order to have a reasonable self-consistency procedure you still need k+q = k'+G. Try to do it, and you will see why :) > Moreover, and this is the main problem, I don't know how > to make them compatible. Once I have chosen a certain dimension of the > Monkhorst-Pack grid (nk1=nk2=nk3=K) which values can I give to > nqx1=nqx2=nqx3 ? Is there an a-priori argument? You can set nqx* to any integer Q divisor of K, i.e. nqx1=Q with Q*N = K with N integer. > Another error message that I get is "Error in routine electrons (1): > dexx is negative! Check that exxdiv_treatment is appropriate for the > system" in the calculation with B3LYP, while HSE seems working well up to a > certain cutoff, after which the error appears . I read that somebody solved > it changing exxdiv_treatment, but I don't if or why I should do that, or if > it is related to my "manual" choice of q-grid. Any suggestion? You will have to try both, I guess. HTH -- Dr. Lorenzo Paulatto IdR @ IMPMC -- CNRS & Université Paris 6 +33 (0)1 44 275 084 / skype: paulatz http://www.impmc.upmc.fr/~paulatto/ 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05 _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
