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Dear Lorenzo,<br>
thanks for your answer. I still have some doubts; when you say that
<br>
<pre>'In the limit where the {q} grid contains only the Gamma point, than
each k-point exchanges only with itself (not with Gamma!).'</pre>
it means that the q+k grid will end up to be the k grid. But then, <br>
<pre>'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. '</pre>
which is the difference with this second case? I have thought that
when q grid and the k grid have the same spacing, the number of k+q
points is larger than that of the k points, so they could not be
equivalent. <br>
As you see, I am a beginner and a bit confused about this topic, do
you have any paper to recommend me? <br>
Thank you very much,<br>
regards<br>
<br>
Valentina<br>
<br>
<br>
Il 04/15/2013 01:08 PM, Lorenzo Paulatto ha scritto:<br>
<blockquote cite="mid:516BDFB6.5030409@impmc.upmc.fr" type="cite">
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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>
</div>
<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 moz-do-not-send="true" class="moz-txt-link-freetext" href="http://www-int.impmc.upmc.fr/%7Epaulatto/">http://www-int.impmc.upmc.fr/~paulatto/</a>
mail: 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 5</pre>
</blockquote>
<br>
<br>
<div class="moz-signature">-- <br>
<img src="cid:part2.03060109.05030806@tirocinanti.crf.it"
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