# [Pw_forum] Charge density Grid

Paolo Giannozzi paolo.giannozzi at uniud.it
Tue Aug 5 22:51:20 CEST 2014

```On Tue, 2014-08-05 at 11:33 -0400, Kayahan Saritas wrote:

> pp.x document says that I can use output_format = 3 to manipulate grid
> density, otherwise grid density is taken from FFT grid (or Fourier
> components are used), however it doesn’t seem to work even though I
> tried all possible 3D options for output_format.

when everything else fails, read the ... code:

! are vectors defining the plotting region aligned along xyz ?
!
fast3d = ( e1(2) == 0.d0  .and.  e1(3) == 0.d0) .and. &
( e2(1) == 0.d0  .and.  e2(3) == 0.d0) .and. &
( e3(1) == 0.d0  .and.  e3(2) == 0.d0)
!
! are crystal axis aligned along xyz ?
!
fast3d = fast3d .and. &
( at(2,1) == 0.d0  .and.  at(3,1) == 0.d0) .and. &
( at(1,2) == 0.d0  .and.  at(3,2) == 0.d0) .and. &
( at(1,3) == 0.d0  .and.  at(2,3) == 0.d0)

fast3d = fast3d .and. (trim(interpolation) == 'fourier')
!
!    Initialise FFT for rho(r) => rho(G) conversion if needed
!
IF (.not. ( iflag == 3 .and. ( output_format == 5 .or. &
output_format == 6 .or. &
fast3d ) ) ) THEN
the case you want is active if the above is true. If you have
set iflag == 3 and output_format == 3 or 4 and it still doesn't
work, this means that "fast3d" is true, which happens if both the
desired axis and the crystal axis lie along the three cartesian
axis. Since the code tries hard not to use Fourier interpolation
in 3D (it is awfully slow), in this case the entire grid is chosen.
This is however not consistent with what the documentation says,
though. You may either modify the code the hard way, or try
"interpolation='bspline'"

P.

>
>
> Input file:
>
>
> &INPUTPP
> outdir='./'
> prefix='in'
> plot_num=0
> spin_component=0
> filplot='tmp_dens'
> /
> &PLOT
> nfile=1
> output_format=3
> fileout='density.xsf'
> iflag=3
> e1(1)=1.0, e1(2)=0.0, e1(3)=0.0,
> e2(1)=0.0, e2(2)=1.0, e2(3)=0.0,
> e3(1)=0.0, e3(2)=0.0, e3(3)=1.0,
> x0(1)=0.0, x0(2)=0.0, x0(3)=0.0,
> nx=144, ny=144, nz=144
> /
>
>
> Thanks,
>
>
> Saritas Kayahan
> PhD Student
> Grossman Group
> Office: 13-4069
> Cell: +1-617-955-3981
> Office: +1-617-258-8741
> Email: kayahan at mit.edu
>
>
>
>
>
>
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> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

--
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

```

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