Subject: CCL: Correlation effect on ....

From: "Jens Spanget-Larsen" <[email-masked]>
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: <[email-masked]>
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