THEORETICAL-STUDIES FOR 2ND HYPERPOLARIZABILITIES OF ALTERNANT AND CONDENSED-RING CONJUGATED SYSTEMS .2.

Alternant and condensed-ring conjugated systems are expected to have l arge electron correlation and structure dependencies of the second hyp erpolarizabilities (gamma). For example, cation radical triafulvalene exhibits a large negative gamma at the Hartree-Fock (HF) level contrar y to a large positive one at the Muller-Plesset second-order (MP2) lev el. In this paper, we investigate gamma's for different charged states (neutral, ion radical and di-ion states) of pentalene and triafulvale ne to reveal their electron correlation dependencies up to the Muller- plesset fourth order.