Exploring the boundary between aromatic and olefinic character: Bad news for second-order perturbation theory and density functional schemes
- Univ. of Georgia, Athens, GA (United States)
- Swiss Center for Scientific Computing, Zuerich (Switzerland)
The question whether [10]annulene prefers olefinic structures with alternate single and double bonds or aromatic structures like all other small to medium sized uncharged (4n + 2){pi} electron homologs (e.g. benzene, [14]annulene) has been controversial for more than 20 years. Our new results suggest that only the high-order correlated methods will be able to correctly predict the [10]annulene potential energy surface. The UNO-CAS results and the strong oscillation of the MP series show that nondynamical electron correlation is important. Consequently, reliable results can only be expected at the highest correlated levels like CCSD(T) method, which predicts the olefinic twist structure to be lower in energy by 3-7 kcal/mol. This prediction that the twist structure is lower in energy is supported by (a) the MP2-R12 method, which shows that large basis sets favor the olefinic structure relative to the aromatic, and (b) the fact that both structures are about equally affected by nondynamical electron correlation. We conclude that [10]annulene is a system which cannot be described adequately by either second-order Moller-Plesset perturbation theory or density functional methods. 13 refs., 3 tabs.
- DOE Contract Number:
- FG05-94ER14428
- OSTI ID:
- 263145
- Journal Information:
- Journal of the American Chemical Society, Vol. 118, Issue 14; Other Information: PBD: 10 Apr 1996
- Country of Publication:
- United States
- Language:
- English
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