Web Release Date: November 5,
Conformations of [10]Annulene: More Bad News for Density Functional Theory and Second-Order Perturbation Theory
and
Contribution from the Center for Computational Quantum Chemistry, Department of Chemistry, The University of Georgia, Athens, Georgia 30602-2525, and Institute for Theoretical Chemistry, Departments of Chemistry and Biochemistry, The University of Texas, Austin, Texas 78712-1167
Received May 3, 1999
Revised Manuscript Received August 30, 1999
Abstract:
The molecular structures and relative energies of several of the lowest-energy conformations of
[10]annulene (C10H10) have been investigated using the Hartree-Fock (HF) method, density functional theory
(DFT), second-order M
ller-Plesset perturbation theory (MP2), and (for the first time) coupled cluster singles
and doubles with a perturbative inclusion of connected triple excitations [CCSD(T)]. For some years the HF
method has been known to incorrectly favor bond-length-alternating structures for [10]annulene, and standard
forms of DFT are now seen to incorrectly favor aromatic structures. For the naphthalene-like conformation,
the B3LYP method is shown to require a large basis set before the geometry becomes properly bond-localized,
i.e., similar to the predictions of CCSD(T) using even a modest basis set. With a basis set of 170 functions,
B3LYP and BP86 predict that the aromatic heart-shaped conformation is 9.11 and 12.11 kcal mol-1, respectively,
lower than the bond-alternating twist form, while with the same basis set CCSD(T) places the heart-shaped
conformation 6.29 kcal mol-1 above the twist. Further large-scale CCSD(T) computations involving 340 basis
functions predict that the twist conformation is lowest in energy, and the naphthalene-like and heart-shaped
conformations lie higher than the twist by 1.40 and 4.24 kcal mol-1, respectively. Implications of the computed
structures and energetics for the interpretation of previous experiments are discussed.
Download the full text: PDF | HTML
