Subject: Re: CCL:Charges/bond-breaking

From: Frederic BOUYER <[email-masked]>
Date: Mon, 24 Apr 1995 18:47:13 +0100

Dear Simon,

If you are using HF(Hartree-Fock) or DFT methodology, I will recommend UHF
calculations, since like H2 (see A. Szabo et N. S. Ostlund, Modern Quantum
Chemistry, Introduction to Advanced Electronic Structure Theory, Mc
Graw-Hill, New-York, 1989), one single electron is localized on each atom.
A RHF calculation will produce an overestimated energy (beginning a given
interatomic distance, not at the stable structure) since it will force the
two electrons (for H2) to be in the same molecular orbital.

I will recommend too to take into account the effect of the correlation:
MP2 (or n) or CI (if you can) for Hartree-Fock; for DFT techniques,
correlations are taken into account (even at VWN level of calculations),
the best will be (I think) Becke+Lee-Yang-Parr (gradient correction
methods). The aim is to take into account different possible states (the
fact that one electron could be on one level of energy or one other, with
the HF point of view) in the global wave function.

Take the same procedure to calculate all your potential energy surfaces, so
that all energies can be comparable, for calculating energy reactions, or
energy barriers for the dissociations.

That is all I can say, at the moment, roughly speaking. Tell me if I am
wrong. I am very interested in sharing with you, if it is possible, all the
replies you could receive.

Thank you in advance.

Regards,
Frederic Bouyer

______________________________________________________________________________
Frederic BOUYER
Laboratoire d'Electrochimie et de Chimie Analytique
Equipe "Reactivite en Milieux Ioniques Liquides" (G. PICARD)
ENSCP
11, rue Pierre et Marie Curie
75231 PARIS Cedex 05
FRANCE
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Fax : (33)-1-44-27-67-50
E-mail : [email-masked]
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http://alcyone.enscp.jussieu.fr/Pages/LECA/GP/frederic.html

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