[Pw_forum] shape of the wave function in reciprocal space

[Paolo Giannozzi]

Only plane waves with \hbar^2(k+G)^2/(2m) < Ecut are included. The
regular grid in G-space must be large enough to include all of them,
but it also includes a significant amount of plane waves that exceed
the cutoff.

Paolo

On Fri, May 26, 2017 at 2:46 AM, Jacopo Simoni <simonij at tcd.ie> wrote:
> Dear PWSCF users,
>
> I am doing a simple scf calculation for a system of 100 Hydrogen atoms in a
> simple cubic cell.
>
> I am generating the wave functions with wf_collect=.true. for a single K
> vector (0,0,0).
>
> From the scf output I realized that the total number of G vectors printed on
> the file is 847. I am using ecutwfc=20.0 and the shape of the Kohn-Sham
> matrix is
>
> Kohn-Sham wave functions    dimensions=(847, 52)
>
> where 52 corresponds to the number of bands that I am using in the
> calculation.
>
> However, I am wondering why in the gkvectors.xml file I have a list of G
> vectors ranging between -5 and 5 times 2*pi / a (a is the lattice parameter)
> along each primitive lattice direction.
>
> The total number of points in such a regular grid should be 11*11*11 = 1331
> that is clearly different from 847. What is the meaning of the missing 484 G
> vectors in the grid ? I am a bit confused could you please explain to me
> these results ?
>
> Many thanks in advance,
>
> Jacopo Simoni,
> Los Alamos National Laboratory
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222