[QE-users] Calculating the total (valence + core) charge

[Paolo Giannozzi]

On Tue, Oct 2, 2018 at 11:46 AM Jan Oliver Oelerich <
jan.oliver.oelerich at physik.uni-marburg.de> wrote:

What you say makes sense, but doesn't it render the plot_num=21 feature
> kind of useless then?
>

from the documentation:
                   21 = all-electron charge density (valence+core).
                        For PAW calculations only; requires a very dense
real-space grid.

If you just need a plot, in particular a 1D plot, you may try code
"pawplot".

BTW, using the plot_num=0 for the pseudo charge density also doesn't
> give me reasonable results, possibly for the same reason. I guess I need
> finer grids even for that case?
>

no, you should get a very reasonable plot with the FFT grid used in the
calculation

Ultimately I am interested in the total charge density of my system
> (including positive charges from the cores); Am I correct that this is
> difficult to obtain using QE?
>

the problem is not QE, it is the plane wave basis set

Paolo

>
> Cheers!
>
>
> On 10/2/18 11:37 AM, Alberto Otero de la Roza wrote:
> > Hi Jan,
> >
> > That is normal for the all-electron density. The density peaks at the
> > nuclei are very steep, so they are poorly represented by a uniform
> > grid and consequently the cube doesn't integrate to the correct number
> > of electrons. You can try to make the grid finer but for most systems
> > that won't help very much because you would need an unreasonable
> > number of grid points to converge it.
> >
> > Best,
> >
> > Alberto
> >
> > --
> > Dr. Alberto Otero de la Roza
> > Department of Physical and Analytical Chemistry,
> > University of Oviedo
> >
> >
> > * Jan Oliver Oelerich <jan.oliver.oelerich at physik.uni-marburg.de>
> [2018-10-02 11:28:05 +0200]:
> >> Hi QE users,
> >>
> >> I need the total charge density (including core electrons) and
> calculated it
> >> using pp.x's `plot_num=21` method after a converged SCF calculation.
> (See
> >> below for the pw.x and pp.x input files).
> >>
> >> Summing up the values of the `density.cube` file and multiplying the
> result
> >> with the volume element (dV=V/(96*96*180), V in bohr^3) gets me nothing
> even
> >> close to the expected value of 76 electrons. (I get 2.7..)
> >>
> >> What am I missing here? Are my grids too small or is it something about
> the
> >> units that I got wrong?
> >>
> >> Thanks and cheers,
> >> Jan Oliver Oelerich
> >>
> >> -------pw.x----------
> >> &CONTROL
> >>      calculation = 'scf',
> >>      prefix     = 'GaN',
> >>      pseudo_dir = '/opt/QEPseudos/pslibrary.1.0.0/pbe/PSEUDOPOTENTIALS',
> >>      outdir     = './out',
> >>      wf_collect = .TRUE.,
> >> /
> >> &SYSTEM
> >>      ecutwfc          = 30.0
> >>      ntyp             = 2
> >>      nat              = 4
> >>      ibrav            = 0
> >>      nr1              = 96
> >>      nr2              = 96
> >>      nr3              = 180
> >> /
> >> &ELECTRONS
> >> /
> >>
> >> ATOMIC_SPECIES
> >> Ga 69.723   Ga.pbe-dn-kjpaw_psl.1.0.0.UPF
> >> N  14.007   N.pbe-n-kjpaw_psl.1.0.0.UPF
> >>
> >> K_POINTS automatic
> >> 6 6 4  0 0 0
> >>
> >> CELL_PARAMETERS angstrom
> >> 3.18600000000000 0.00000000000000 0.00000000000000
> >> -1.59300000000000 2.75915693645722 0.00000000000000
> >> 0.00000000000000 0.00000000000000 5.18600000000000
> >>
> >> ATOMIC_POSITIONS angstrom
> >> Ga 0.0000000000 0.0000000000 0.0000000000
> >> N 0.0000000000 1.8394379576 0.6440642113
> >> Ga 0.0000000000 1.8394379576 2.5930000000
> >> N 0.0000000000 0.0000000000 3.2370642113
> >>
> >>
> >> -------pp.x------------
> >> &inputpp
> >>      prefix  = 'GaN'
> >>      outdir = './out'
> >>      filplot = 'electron_density.dat'
> >>      plot_num = 21
> >> /
> >> &plot
> >>      nfile = 1
> >>      filepp(1) = 'electron_density.dat'
> >>      weight(1) = 1.0
> >>      iflag = 3
> >>      output_format = 6
> >>      fileout = 'density.cube'
> >> /
> >>
> >>
> >> --
> >> Dr. Jan Oliver Oelerich
> >> Philipps-Universität Marburg
> >>
> >> Faculty of Physics and Material Sciences Center
> >> Addr.: Room 02D35, Hans-Meerwein-Straße 6, 35032 Marburg, Germany
> >> Phone: +49 6421 2822260
> >>
> >> Semiconductor Theory, Department of Physics
> >> Addr.: Room 01001, Mainzer Gasse 33, 35032 Marburg, Germany
> >> Phone: +49 6421 2824335
> >>
> >> Mail : jan.oliver.oelerich at physik.uni-marburg.de
> >> Web  : http://academics.oelerich.org
> >>
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>
> --
> Dr. Jan Oliver Oelerich
> Philipps-Universität Marburg
>
> Faculty of Physics and Material Sciences Center
> Addr.: Room 02D35, Hans-Meerwein-Straße 6, 35032 Marburg, Germany
> Phone: +49 6421 2822260
>
> Semiconductor Theory, Department of Physics
> Addr.: Room 01001, Mainzer Gasse 33, 35032 Marburg, Germany
> Phone: +49 6421 2824335
>
> Mail : jan.oliver.oelerich at physik.uni-marburg.de
> Web  : http://academics.oelerich.org
>
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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
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