# CCL: Correlation effect on ....

*From*: "Jens Spanget-Larsen" <spanget ^at^
virgil.ruc.dk>
*Organization*: Roskilde Universitetscenter
*Subject*: CCL: Correlation effect on ....
*Date*: Thu, 28 Feb 2002 09:17:35 +0100

"Students of Dr. S. R. Gadre":
> CCLer's...
> Could somebody give me a concrete example of weakly interacting
> geometrical conformers where the energy trends reverse in correlated
> methods.( One of the weakly interacting geometrical conformers which
> was a lower energy minimum at Hartree Fock level should not be a
> lower energy minimum in a correlated method like MP2 ...a conformer
> which was not a lower energy minimum in Hartree Fock becoming a
> lower energy minimum with a correlated method is the kind of
> situation that i am looking for...the structures should be
> stationary points on the PES)
Dear Bala,
the example of 1,6,6a-trithiapentalene may be of interest to you. Ab
initio Hartree-Fock theory predicts an equilibrium geometry of Cs
molecular symmetry, corresponding to a situation with two equivalent
Cs symmetrical valence tautomers separated by a barrier of about 10
kcal/mol. Introduction of electron correlation effects (MP2, DFT)
leads to the prediction of a single C2v symmetrical equilibrium
geometry, consistent with the experimental evidence:
K. B. Andersen, J. Abildgaard, J. G. Radziszewski, J. Spanget-Larsen,
J. Phys. Chem. A 101, 4475 (1997)
J. Spanget-Larsen, K. B. Andersen, Phys. Chem. Chem. Phys. 3, 908
(2001)
Yours, Jens >--<
NB! Please note new mail address: <spanget ^at^ ruc.dk>
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