ChemInform Abstract: Cluster Expansion of the Wave Function. Valence and Rydberg Excitations and Ionizations of Benzene

Abstract

The SAC (symmetry‐adapted cluster) expansion and the SAC‐CI theory are applied to the calculations of the valence and Rydberg excitations and the ionizations of benzene. The active space consists of 80 MO’s including both π and σ spaces; viz., 35π+45σ for the valence excitations and ionizations and 29π+51σ for the Rydberg excitations. For the lower six valence excited states, 3B1u(T1), 3E1u(T2), 1B2u(S1), 3B2u(T3), 1B1u(S2), and 1E1u(S3), generated from the π(e1g)→π*(e2u) transitions, the excitation energies are reproduced to within 0.5 eV of the experimental values with the average discrepancy being 0.34 eV. The first three states are explainable within the π electron space. For the other three states, the σ‐reorganization effect is very important; viz., 0.6, 0.7, and 0.8 eV for the T3, S2, and S3 states, respectively. The polarizationdπ function also works to lower the T3 and S2 states by 0.3 and 0.4 eV, respectively. The total lowerings from the SDT π‐CI of Hay and Shavitt to the 35π+45σ SAC‐CI are abo...