[Pw_forum] Question about electron (pseudo-)charge density calculations in QE

[reza vatan]

Dear Paolo and Stefano,

Thank you so much for your reply.
Both ways give me the same values but still incorrect value which is 8
electron per unit cell however I have only 2 electron per unit cell. Is it
possible that QE is giving me charge density in a unit different than
e/bhor^3 unit?

 Paolo! I only have one hydrogen molecule per unit cell. Following is my
input file:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 &control
    prefix='h2-scf',
    pseudo_dir='./'
    outdir = './',
    wf_collect=.true.,
    verbosity ='high',
 /
 &system
ibrav = 6, celldm(1) =20.37, celldm(3) =1.0,   nat  =2, ntyp=1,
    ecutwfc = 12.0,
    ecutrho = 100,
    nbnd=10,
  degauss     = 0.05D0,
  occupations = "fixed",
  smearing    = "methfessel-paxton",
    force_symmorphic= .true.
 /
 &electrons
 /
ATOMIC_SPECIES
 H  1.01  Si.blyp-hgh.UPF
ATOMIC_POSITIONS (angstrom)
H        0.099985299   0.099985299   0.077144425
H        0.100014701   0.100014701   0.862855575
K_POINTS {automatic}
4 4 4 0 0 0
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Best,
Reza

On Wed, May 25, 2016 at 10:40 PM, Stefano de Gironcoli <degironc at sissa.it>
wrote:

> Dear Reza Vatan,
>       In order to canculate the total charge you should sum the density on
> all point and multiply the result by the volume element. That is multiply
> by 20.37^3 and divide by 45^3 or 72^3 depending on the grid used.
> Which gives 8 in both cases
>
> Di you place 4 molecules in the unit cell ?
>
> stefano
> (sent from my phone)
>
> > On 26 May 2016, at 01:44, reza vatan <rezavatan64 at gmail.com> wrote:
> >
> > Dear all,
> >
> > I have one hydrogen molecule in a unit cell repeating in 3D space in
> such a way non of the hydrogen molecules can't see each other. I'm trying
> to calculate the "electron (pseudo-)charge density" in the entire unit cell
> using pp.x. The problem is that when I add the charge density of all meshes
> to get the total charge density of the entire unit cell I get different
> values depends on the used grid. For instance, when I use 45x45x45 grid I
> get 86.25 for charge density, but when I use 72x72x72 I get 353.26.
> >
> > However, since my unit cell size is 20.37x20.37x20.37 bhor^3 and I have
> 2 electrons in the unit cell, I think I should get
> 2/(20.37x20.37x20.37)=0.000236623. Does any one know why I'm not getting
> this number?
> >
> > Thanks in advances,
> >
> > Best,
> > Reza Vatan,
> > Electrical Engineering Department,
> > Arizona State University.
> > _______________________________________________
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> > Pw_forum at pwscf.org
> > http://pwscf.org/mailman/listinfo/pw_forum
>
>
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