CCL: Correlation effect on ....

"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
 Yours, Jens >--<
 NB! Please note new mail address: <spanget ^at^>
 JENS SPANGET-LARSEN         Office:         +45 4674 2710
 Department of Chemistry     Fax:            +45 4674 3011
 Roskilde University (RUC)   Mobile:         +45 2320 6246
 P.O.Box 260                 E-Mail:        spanget ^at^
 DK-4000 Roskilde, Denmark