AB-INITIO STUDIES OF THE DIPOLE POLARIZABILITIES OF CONJUGATED MOLECULES .1. ETHENE AND BENZENE

We report an accurate and systematic ab initio SCF MO study of the mol ecular geometry and the static dipole polarizability of ethene and ben zene. The sensitivity of polarizability calculation to the effects of the geometry optimizations, the choice of basis set and to the inclusi on of electron correlation at the MP2 level was studied. The basis set s were constructed by extension of the STO/6-31G of STO/6-311G with di ffuse s and p functions and multiple d and p polarization functions, g iving the STO/6-31+ (nd,mp) and STO/6-311 + G(nd,mp) scheme. We show t hat these basis sets, with n = m = 3, lead to SCF and MP2 polarizabili ty values for ethene and SCF polarizability for benzene that are in ex cellent agreement with the available theoretical and experimental data . We also found that the effect of MP2 correlation on the polarizabili ty calculations, which are greater in ethene than benzene, decrease wh en the number of polarization functions is increased in the diffuse ba sis set.