From NWChem
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2:24:47 PM PDT  Wed, Oct 16th 2013 

I am a little puzzled by the cube files that I get when I use the following command to produce a Gaussian cube file with the total electron density:
dplot
gaussian
title monomer_12ang_anion_charge_density33
output monomer_12ang_anion_charge_density33.cube
vectors C70.movecs
spin total
LimitXYZ
7.5 7.5 150
7.5 7.5 150
16.5 16.5 330
end
task dplot
I've been using some MATLAB code to process the cube files and decided to sum all data points in one of these density files to confirm that it adds up to the number of electrons. It does not; for a system of 421 electrons the sum of all the data points in the cube file is about 58,000. If I use the same value of the rangeseparation parameter (I use rangeseparated functionals), the sum of the numbers in the cube file is always about 58,000, with variations of 0.10.2% from this number. If I change the value of the rangeseparation parameter, the sum changes to about 61,000.
I seem to be missing something, I would have thought that a charge density file should sum to the number of electrons. Could anyone explain to me what DPLOT is doing here?
Thanks in advance for any advice.




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3:21:23 PM PDT  Thu, Oct 17th 2013 

Integration volume

Kenley,
Does your MATLAB code include the integration volume?
In your case, the integration volume is
(15./150.)^2*(33./330.)/(.529177)^3=.0067483
If you multiply .0067483*60,000 you get 405, that is not so far off your 421 number of electrons.



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