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

[stefano de gironcoli]

Dear Reza,
    the integrated density is computed in many places giving the right 
result.
    check your code with some of these places. for instance when Hartree 
potential is computed in PW/src/v_of_rho.f90

stefano

On 26/05/2016 21:56, reza vatan wrote:
> 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 <mailto: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
>     <mailto: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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