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<div class="moz-cite-prefix">On 04/15/2013 12:23 PM, "Valentina
Dellacà C.R.F. S.C.p.A." wrote:<br>
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<blockquote cite="mid:516BD51B.8020402@tirocinanti.crf.it"
type="cite">
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Hi,<br>
I am having some doubts concerning nqx1,2,3 and K points grid when
using hybrid functionals. As I understand, please let me know if I
am wrong, there is no specific rule in how to choose the q point
grid, for a given k point grid. The advice is to choose them to be
the same, in order to avoid convergence issues. My question now
is, since I read in hybrid functional README, that a shift in the
q point grid is not implemented, can I pick a shifted k-point grid
and a non shifted q point grid? Would it be better to pick two
unshifted grids?<br>
</blockquote>
<br>
Dear Valentina,<br>
the grids are {k} and {k+q}, where the {q} grid is always
Gamma-centered. In other words, for each k point there is a
corresponding {k+q} grid centered around it.<br>
<br>
There is the additional constraint that each k+q point (for every k
and q) must be related to one of the initial k points by a G vector
of the reciprocal lattice and eventually a symmetry operation. I
think this condition should not cause any problem if the {k} grid is
shifted, but I'm not 100% sure.<br>
<br>
In the limit where the {q} grid contains only the Gamma point, than
each k-point exchanges only with itself (not with Gamma!). In the
opposite limit where the {q} grid has the same spacing as the {k}
one (which may include a shift) then the {k} grid becomes equivalent
to the {k+q} one, for every k. I.e. the {k} grid and any {k+q} grid
are just shifted and re-indexed w.r.t each other. <br>
<br>
I hope this helps, it is a bit confusing but it makes sense
eventually.<br>
<br>
bests <br>
<br>
<pre class="moz-signature" cols="72">--
Dr. Lorenzo Paulatto
IdR @ IMPMC -- CNRS & Université Paris 6
phone:+33 (0)1 44275 084 / skype: paulatz
www: <a class="moz-txt-link-freetext" href="http://www-int.impmc.upmc.fr/~paulatto/">http://www-int.impmc.upmc.fr/~paulatto/</a>
mail: 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 5</pre>
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