A SEMIEMPIRICAL APPROACH TO NONLINEAR-OPTICAL PROPERTIES OF LARGE MOLECULES AT THE MNDO AND MNDO D LEVEL/

The analytical evaluation of polarizabilities (alpha) and hyperpolariz abilities (beta, gamma) has been implemented for semiempirical wavefun ctions using the coupled Hartree-Fock technique. For molecules with se cond-row and heavier atoms, the results from MNDO/d are superior to th ose from MNDO. The basis set at hydrogen has been extended to include 2p functions, and the corresponding additional parameters have been op timized with respect to experimental polarizabilities and hyperpolariz abilities. The resulting specialized MNDO and MNDO/d treatments provid e reasonable values for alpha and reproduce trends in gamma, but are n ot useful for beta. Perspectives for future work are outlined.