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

  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
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