NDDO-BASED CI METHODS FOR THE PREDICTION OF ELECTRONIC-SPECTRA AND SUM-OVER-STATES MOLECULAR HYPERPOLARIZATION

NDDO-based (AM1) configuration interaction (CI) calculations have been used to calculate the wavelength and oscillator strengths of electron ic absorptions in organic molecules and the results used in a sum-over -states treatment to calculate second-order-hyperpolarizabilities. The results for both spectra and hyperpolarizabilities are of acceptable quality as long as a suitable CI-expansion is used. We have found that using an active space of eight electrons in eight orbitals and includ ing all single and pair-double excitations in the CI leads to results that agree well with experiment and that do not change significantly w ith increasing active space for most organic molecules. Calculated sec ond-order hyperpolarizabilities using this type of CI within a sum-ove r-states calculation appear to be of useful accuracy.