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

Stefano de Gironcoli degironc at sissa.it
Thu May 26 07:40:15 CEST 2016

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 ?

(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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