[Pw_forum] shape of the wave function in reciprocal space

[Jacopo Simoni]

Many thanks for the answer.

This means that the G+k points written in the gkvectors.xml file are the
ones such that

\hbar^2|k+G|^2/(2m) < Ecut

and they form a sphere not a parallelepiped
I am right ?

On 25 May 2017 at 23:49, Paolo Giannozzi <p.giannozzi at gmail.com> wrote:

> 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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> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
>
>
>
> --
> 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
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>
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