Exponentially generated wave functions and excited states of benzene

Abstract

Usefulness of the exponentially generated wave function approach is shown. We first give an overview of the SAC (symmetry adapted cluster) and SAC-CI study on the valence and Rydberg excitations and ionizations of benzene including both π and σ spaces. The importance of the σ reorganization effect is found for the T3(3B2u), S2(1B1u), and S3(1E1u) states, so-called V states. A first systematic calculation is reported for the Rydberg excited states. Next, the idea of the exponentially generated wave function (EGWF) theory is explained. New exponential-type operators and new wave functions associated with them are defined. The mixed or multi use of these exponential operators is shown to be effective both physically and practically. We call the resultant wave functions MEG (multi-exponentially generated) wave functions. We then explain the algorithm of calculations and show some results on the potential energy curves of the ground, excited, and quasi-degenerate states of some diatomics and triatomics.