[QE-users] Meaning of three G vectors sets

[Lorenzo Paulatto]

> Parallelization info
>
> --------------------
>
> sticks: densesmooth PW G-vecs:dense smoothPW
>
> Min 287 287 819007990079 13189
>
> Max 288 288 829013090130 13206
>
> Sum25872587733 810915 810915118781
>

Hello Lorenzo,

the G-vecs are the plane waves, the 3x3 table gives the maximum and 
minimum number per CPU and the total number for the charge density grid 
(ecutrho), the "smooth" (4xcutwfc) grid, and the plane-wave (ecutwfc) grid.

The sticks, are the subdivisions of the plane waves over which the 
parallelization occurs, i.e. the charge is subdivided in 2587 sticks and 
every CPU inside a pool gets 287 or 288 to do Fourier transforms (they 
used to be called planes, I guess it now depends if you are using 
"pencil decomposition" or not)

> Second, when printing the energies per k-point, a number of G vectors 
> is given as if it were the number of planewaves ( e.g. "k = 0.0833 
> 0.1443 0.0000 (101603PWs) bands (ev):" ). What does this number 
> actually refer to?
>
It is in fact the number of plane waves used to expand the wvafunction 
at that k-point.

The condition to include a plane wave is that (G+k)^2 < ecutwfc/ħ, which 
defines a sphere in reciprocal space, with G being a multiple of the 
reciprocal axis vectors and k is smaller than any G. So the number 
varies with the k-point. Then, in order to do FFT, all he G from all the 
spheres are combined and padded with extra point to make a parallelogram.

You take a parallelogram of twice the side in order to fit |psi|^2, and 
if a larger ecutrho has been defined this will determine a third grid 
with |G|^2 < ecutrho/ħ

hth

> Last question: how all these sets are related to the values of ecutwfc 
> and ecutrho ?
>
should be explained above.


> Many thanks!
>
>
> -- 
> Dr. Lorenzo Sponza
>
> Chargé de Recherche au CNRS
> Université Paris-Saclay, ONERA, CNRS Laboratoire d'étude des 
> microstructures (LEM)
> 29 Avenue de la division Leclerc, 92322 Châtillon
> Tel: +33146734464
>
> ETSF Research Team Leader
> European Theoretical Spectroscopy Facility
> 17 Sart-Tilman B-4000 Liège, Belgium
>
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-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
phone: +33 (0)1 442 79822 / skype: paulatz
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