From owner-chemistry # - at - # ccl.net Tue Sep  8 09:05:01 2015
From: "=?iso-8859-1?Q?V=EDctor_Lua=F1a?= Cabal victor===fluor.quimica.uniovi.es" <owner-chemistry],[server.ccl.net>
To: CCL
Subject: CCL:G: Electronic potential g09 output
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Date: Tue, 08 Sep 2015 14:46:52 +0200
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Sent to CCL by: =?iso-8859-1?Q?V=EDctor_Lua=F1a?= Cabal [victor**fluor.quimica.uniovi.es]
On Tue, Sep 08, 2015 at 06:33:02AM -0400, Sara Tortorella sara::chemiome.chm.unipg.it wrote:
> 
> Sent to CCL by: "Sara  Tortorella" [sara{}chemiome.chm.unipg.it]
> Hi everyone,
> I'm new to this forum (...and also to computational chemistry!), so I'm wondering if you could help me in clarifying the electrostatic properties section of gaussian 09 output.
> In particular, I'm performing B3LYP/6-31g* Pop=MK or Pop=CHelpG in order to obtain an estimation of atomic charges. Below you can see the output I get.
> The question is: how is the electric potential reported below the charges (from  '1 Atom    -14.652466' to the end) exactly calculated? It is the same I could get with the cubegen potential utility (but in different units)? Is it the potential the MK or CHelpG charges are trying to fit? 
> Any references will be appreciated!

Sara,

Obtaing the electrostatic potential from the charges is an awful approach.
The electrostatic potencial is

$ \int \frac{D(r') dr'}{\abs{r-r}} $

where D(r') is the total charge density (i.e. electronic plus nuclear).

You can approach the potential by a multipolar dixtribution, but that
includes terms from 0-poles (charges), 2-poles (dipoles), 4-poles,
and all the collection of 2^L poles up to the desired accuracy.

The cubegen utility provides you the Molecular electrostatic potential,
and it is given in atomic units (electrons per cube bohr). That can be
depicted with codes like vmd, and analyzed with tools like critic2.
There are many others.

The electron density and the EP are related through the Poisson equation,
and solving it is another way for obtaing the EP.

A book on the subject is

book{QCB-MurraySen1996,
  editor = "Murray, J. S. and Sen, K.",
  title = "Molecular electrostatic potentials",
  serie = "Theoretical and computational chemistry",
  volume = 3,
  publisher = "Elsevier",
  pages = 661,
  isbn = "0444823530",
  }

Peter Politzer and Jane S. Murray have been working on the molecular
EP for *many* years.

Best regards,
             Dr. Víctor Luaña
--
     .  .    "In science a person can be convinced by a good argument.
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   /(o)(o)\  (Adapted from Carl Sagan)
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 |  \'`'`/  | actitud" -- Jorge Wasenberg, 2015
 |  |'`'`|  | (Mediocre is worse than good, but it is also worse than
  \/`'`'`'\/  bad, because mediocrity is not a grade, it is an attitude)
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