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<div class="moz-cite-prefix">On 04/15/2013 02:33 PM, "Valentina
Dellacà C.R.F. S.C.p.A." wrote:<br>
</div>
<blockquote cite="mid:516BF3A7.1040002@tirocinanti.crf.it"
type="cite">
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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>
</blockquote>
<br>
No, it does not. In fact there is not a single {k+q} grid, there is
one for each k point. In the first case each of these grids contain
a single point: k itself. In the second case, each of this grids
contain all the k points, but in a different order and eventually
translated by a G vector. <br>
<br>
The second condition I stated before guarantees that k+q = Sk'+G,
for every k and q, where k' is a point in the {k} grid, S a symmetry
operation and G a vector of the reciprocal lattice. If you ignore
symmetry, you can restate the condition as, it must be possible to
express any q as q= k-k'+G, same definitions as before.<br>
<br>
This allows to store all the {k+q} grids very efficiently, but you
should still think of them as many different grids.<br>
<blockquote cite="mid:516BF3A7.1040002@tirocinanti.crf.it"
type="cite">As you see, I am a beginner and a bit confused about
this topic, do you have any paper to recommend me? <br>
<br>
</blockquote>
I do not have any paper where this is mechanism is explained in
detail... maybe someone else who's reading this thread can recommend
some reading?<br>
<br>
bests<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 05
</pre>
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