Understanding Gaussian Cube file output by NWChem


Clicked A Few Times
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.

Forum Vet
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

Clicked A Few Times
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)?

Forum Vet
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)



Forum >> NWChem's corner >> General Topics