SIMPLIFIED SUM-OVER-STATES CALCULATIONS AND MISSING-ORBITAL ANALYSIS ON HYPERPOLARIZABILITIES OF BENZENE-DERIVATIVES

The simplified sum-over-states (SOS) and missing-orbital analysis methods are introduced. The former aims to calculate the molecular polarizabilities in the framework of ab initio SCF theory, and the latter to analyze the calculated polarizabilities. The utility of the combination of these methods is demonstrated for the benzene derivatives, e.g. p-nitroaniline (PNA) and p-cyanoaniline (PCA). The calculated first-order hyperpolarizabilities (beta) agree well with those of both CPHF calculations and experimental results. The missing-orbital analysis shows that beta for PCA is contributed by both forward and backward charge transfer (CT) related to ''out-of-plane'' and ''in-plane'' orbitals, respectively. In contrast, beta for PNA is confirmed to be explained fully by the conventional two-state model characterized by strong forward CT.