AB-INITIO STUDIES OF THE DIPOLE POLARIZABILITIES OF CONJUGATED MOLECULES .6. THE GEOMETRY, STATIC DIPOLE POLARIZABILITY AND FIRST HYPERPOLARIZABILITY OF BENZOTHIOPHENE

We report an ab initio study of the geometry and static dipole (hyper) polarizability of benzothiophene in its electronic ground state (1)A'. We fully optimized the geometry both at the HF/3-21G* and HF/6-31G** levels of theory, and we present comparisons with the HF/6-31G* thio phene geometry reported previously. We calculated the dipole (hyper)po larizabilities using an analytic coupled perturbed Hartree-Fock method , with both the STO/6-31+G and STO/6-31G (d,p) basis sets. We analysed the average polarizability in terms of an ''additive polarizabilities '' scheme. We investigated the effects of electron correlation on the dipole moment and the (hyper)polarizabilities, using a fourth-order Ta ylor expansion of the MP2 Moller-Plesset energy and the STO/6-31+G bas is sets, which includes diffuse primitives. Taking as reference the Ha rtree-Fock results, these latter effects account for changes of 29% in the predicted dipole moment and between 3.30% and 5.3% in the predict ed static polarizability components. The correlation effects on the fi rst and second hyperpolarizability components are much bigger.