From chemistry-request@ccl.net Wed Apr 21 09:40:43 2004 Received: from hermes2.cf.ac.uk (hermes2.cf.ac.uk [131.251.0.113]) by server.ccl.net (8.12.8/8.12.8) with ESMTP id i3LEeguR016778 for ; Wed, 21 Apr 2004 09:40:42 -0500 Received: from thor.cf.ac.uk ([131.251.0.1]) by hermes2.cf.ac.uk with esmtp (Exim 4.24) id 1BGIuq-0006me-Rd; Wed, 21 Apr 2004 14:41:32 +0000 Received: from localhost (sacjap@localhost) by thor.cf.ac.uk (8.8.8/8.6.12) with ESMTP id PAA17323; Wed, 21 Apr 2004 15:41:32 +0100 (BST) Date: Wed, 21 Apr 2004 15:41:31 +0100 (BST) From: Jamie Platts X-X-Sender: sacjap@thor To: Mikael Johansson cc: li , "" Subject: CCL:CO dipole moment (was Basis sets for transitional metals) In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Spam-Status: No, hits=1.0 required=7.5 tests=NO_RDNS2 autolearn=no version=2.61 X-Spam-Checker-Version: SpamAssassin 2.61 (1.212.2.1-2003-12-09-exp) on servernd.ccl.net 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