[Pw_forum] shape of the wave function in reciprocal space

[Jacopo Simoni]

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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