[Pw_forum] Units of Charge Density Surfaces Prepared by pp.x as xsf Input to XCrySDen

[Andrei Malashevich]

Paul,

The units are (a.u.)^-3. If you sum up all the values on the
real-space grid and multiply by the volume element dV in atomic units
you should get the number of electrons in the unit cell. (dV =
V/Nx/Ny/Nz, where V is the unit cell volume, Nx, Ny, Nz are dimensions
of the real-space grid).

Best regards,
Andrei

On Tue, Oct 2, 2012 at 9:14 PM, W2AGZ <w2agz at w2agz.com> wrote:
> To All,
>
>
>
> I think I know the answer to this question, but I’d like an expert opinion,
> nonetheless.
>
>
>
> What are the units of “isosurface” plotted by XCrySDen using output from
> pp.x passed through a .xsf file?  I suspect it’s something like
>
> normalized total cell charge (i.e., “e=1 times the number of filled non-core
> pseudo-orbitals per unit cell) divided by a.u.^2.  Suppose I have a
> structure I’m examining with XCrySDen with max/min values, let’s say
> (+3,-1), and I select +0.25.  What exactly is this number in “The Creator’s
> Units,” sometimes known as SI.  I’ve poured through the source code of
> chdens.f, but get lost trying to guess the pneumonic of each variable.
>
>
>
> Seriously, I’m writing up a paper comparing the distribution of charge in
> various (n,m) carbon nanotubes, and want to avoid dumb errors.
>
>
>
> Thanks,
>
>
>
> Paul Grant
>
> W2AGZ Technologies
>
> Associate Staff, JPL/NASA/CalTech
>
>
>
>
>
>
>
>
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