Understanding Gaussian Cube file output by NWChem

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I have been using NWChem to image orbitals in the Gaussian Cube format that I then image in Vesta. I'm a little confused about what the raw numbers that go into the Cube file are. I thought that it was charge density; however, what I get is a file with both positive and negative numbers. Since charge density can't be negative, I am not sure what I am looking at. Could anyone tell me exactly what goes into the cube file? These are for DFT calculations where my dplot section looks like this:


dplot
gaussian
title monomer_4ang1
output monomer_4ang1.cube
vectors C70.movecs
orbitals view;1;211
LimitXYZ
-7.5 7.5 150
-7.5 7.5 150
-8.5 8.5 170
end


The orbitals look reasonable in Vesta, they just have positive and negative lobes. I would be grateful for any explanation of what NWChem is outputting here. Thanks in advance for any advice.

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Kenley,
NWChem is outputting the orbitals values, not the charge densities.
To get the density corresponding to the orbitals # 117 you selected (i.e. the squared value of the orbital),
you need to replace "orbitals view" with "orbitals density", e.g.

orbitals density;1;211

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Thanks Edoapra. So the numbers currently being output in the cube file are simply the square roots of the density at each point (times a factor of +/- 1)?

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Quote:Kpelzer Aug 19th 2:22 pm
Thanks Edoapra. So the numbers currently being output in the cube file are simply the square roots of the density at each point (times a factor of +/- 1)?

No, the correspondence is not so direct.
Here is the formula for the charge density ρ(r) in term of the orbitals ψa(r)

\rho(\mathbf{r}) = \sum_{a=1}^{n_{occ}} |\psi_a(\mathbf{r})|^2
Edited On 2:51:17 PM PDT - Mon, Aug 19th 2013 by Edoapra


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