Subject: CCL:CO dipole moment (was Basis sets for transitional metals)

From: Jamie Platts <Platts{at}Cardiff.ac.uk>
Date: Wed, 21 Apr 2004 15:41:31 +0100 (BST)

Hello Mikael, Liu and all,

  It's not just Mulliken charges! Any charge partitioning scheme will
give a positive C and negative O (except obviously for those constrained
to reproduce the dipole such as Merz-Kollman or CHELPG). Thus Atoms-in-
Molecules, Natural Population Analysis, Lowdin decomp, etc all agree on
the sign, if not the size, of the atomic charges.

  Bader gives a nice explanation of this apparent anomaly in his book
"Atoms in Molecules: A Quantum Theory". Essentially, the C and O electron
densities are polarised within their own basins by the charge transfer
> from C to O, leading to two contributions (inter- and intra-atomic) to the
total dipole moment. CO is a notable case as these are of almost equal
magnitude but opposite sign.

  Hope this helps - Jamie

PS A good reference on dipole moments and other properties of CO is:

Peterson KA, Dunning TH
The CO molecule: The role of basis set and correlation treatment in the
calculation of molecular properties
J MOL STRUC-THEOCHEM 400: 93-117 JUL 10 1997

On Wed, 21 Apr 2004, Mikael Johansson wrote:
>
> On Wed, 21 Apr 2004, li wrote:
> > I am using G98 now, and I am trying to get the electronic structure of
> > CO molecule. By using all the methods implemented in G98, I found that
> > all the result give a similar result - O gets charges from C and has a
> > negative charge. This is quite different from the description I found in
> > books, C should get charge from O and has a negative charge. This makes
> > me confused.
>
> That should not be true. Calculate the dipole moment with some correlated
> methods, and you should get a negative carbon. HF (with a sufficient basis
> set) gets it wrong, though. Don't believe in Mulliken charges here!
>
----------------------------------------------------------
  Jamie Platts
  Dept. of Chemistry  		Phone: +44 (0) 2920 874950
  Cardiff University 	 	Email: platts{at}cf.ac.uk
  P.O. Box 912 			FAX:   +44 (0) 2920 874030
  Cardiff CF10 3TB 		www.cf.ac.uk/chemy