Molecular mechanics-valence bond method for planar conjugated hydrocarbon cations.
We present an extension of the molecular mechanics-valence bond (MMVB) hybrid method to study ground and excited states of planar conjugated hydrocarbon cations. Currently, accurate excited state calculations on these systems are limited to expensive ab initio studies of smaller systems: up to 15 active electrons in 16 pi orbitals with complete active space self-consistent field (CASSCF) theory using high symmetry. The new MMVB extension provides a faster, cheaper treatment to investigate larger cation systems with more than 24 active orbitals. Extension requires both new matrix elements and new parameters: In this paper we present both, for the limited planar case. The scheme is tested for the planar radical cations of benzene, naphthalene, anthracene, and phenanthrene. Calculated MMVB relative energies are in good agreement with CASSCF results for equilibrium geometries on the ground and first excited states, and conical intersections.
Hall
Katherine F
KF
Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom.
Tokmachev
Andrei M
AM
Bearpark
Michael J
MJ
Boggio-Pasqua
Martial
M
Robb
Michael A
MA
D000465:Algorithms; D002412:Cations / Q000737:chemistry*; D003198:Computer Simulation; D006838:Hydrocarbons / Q000737:chemistry*; D019563:Mechanics; D008956:Models, Chemical; D008958:Models, Molecular
D002412:Cations; D006838:Hydrocarbons