[Pw_forum] About the nqx grid on hybrid calculations

[Marcos Veríssimo Alves]

Hi,

I am running some tests with hybrid functionals (pbe0 for the moment, HSE
later), and I have two questions.

1) The first one is about the nqx grid. Should it be defined in the same
way as a Monkhorst-Pack grid would? In my case, I'm running the tests on a
2-D material, so should one of them be equal to one? I am setting my 2-D
material to be contained in the xy plane, so I'm assuming nqx3=1. Is that
assumption correct, or would it lead to nonsense results?

2) The second is also about the nqx grid, but about the convergence of the
calculation, and how to transpose those values for supercells.

Basically, I am reaching convergence in the gap of the material in the unit
cell with a 12x12x1 nqx grid (that is, supposing that nqx can indeed be 1,
in a "Monkhorst-Pack-fashion") - I suppose that larger values for the
nqx(1,2) will not lead to significant differences.

The next step will be to run a calculation for a 6x6 supercell with a
vacancy and see the effect on the electronic charge density and DOS.
However, this will be a very expensive calculation, so I wonder if nqx1 and
nqx2 could be set to lower values on a 6x6 supercell, with a similar result
of that of the unit cell (also similar to what one would do with the
Monkhorst-Pack grid).

Best regards,

Marcos
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