Theoretical studies for second hyperpolarizabilities of alternant and condensed-ring conjugated systems II

Alternant and condensed-ring conjugated systems are expected to have large electron correlation and structure dependencies of the second hyperpolarizabilities (γ). For example, cation radical triafulvalene exhibits a large negative γ at the Hartree-Fock (HF) level contrary to a large positive one at the Møller-Plesset second-order (MP2) level. In this paper, we investigate γʹs for different charged states (neutral, ion radical and di-ion states) of pentalene and triafulvalene to reveal their electron correlation dependencies up to the Møller-plesset fourth order.