[Wien] CHARGE DENSITY --> TOTAL CHARGE

[Laurence Marks]

Rather than giving the answer to the original question, I think it is
better to try and encourage people to solve problems themselves -- perhaps
I am being too much of an teacher, but that is my approach.

So, let me pose a question in response to the original question. What is
the relationship between summing a set of values on a grid and the integral
of a function sampled at a set of grid points. Think about this, and the
reason why the numbers are very different will be obvious.

If they still do not completely agree (they wont), then think about the
accuracy of numerical integration. It is quite important in DFT codes to
remember that numerical integrations are never exact, and this leads to
many small limitations.

On Mon, Oct 12, 2015 at 3:39 AM, Elias Assmann <elias.assmann at gmail.com>
wrote:

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> On 10/08/2015 07:34 PM, prasenjit roy wrote:
> > I want to obtain the total number of electron in the unit cell, by
> > summing over the total charge density within that unitcell and then
> > match that number to the "atomic numbers times the respective
> > multiplicity". Since WIen2K is full electron code, I expect these
> > two be equal.
>
> I have never tried that, but I would expect the number to depend quite
> sensitively on your mesh of r-points.  At least, this is what I saw
> when I looked at normalization of Wannier functions on an r-grid.
> Since you want also the core electrons, you could actually expect even
> larger spikes.
>
> > The system I worked on is : Mn6Fe6Si2P4 (total electron 394 in
> > unitcell). When I summed up all the densities over the mesh (I
> > chose 74*74*80 points), I obtained ~257050.
>
> However, this I would say sounds more like some missing factor …
> Units?  dV?
>
>
>         Elias
>
>
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-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: MURI4D.numis.northwestern.edu
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
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