Class IV charge model for molecular excited states

The intermediate-neglect-of differential-overlap-for-spectroscopy (INDO/S) model for oxygen was reparameterized, thus, yielding a new parameterization called INDO/S2. Following this, two new class IV charge models, CM2/INDO/S and CM2/INDO/S2, were parameterized for 244 dipole moments of both ground and excited states. For a subset of molecules for which comparisons of dipole moments were made, the performance of CM2 was found to be as good as or better than CASSCF calculations for both ground and excited states. The INDO/S2 model was also successful for excitation energies, which have an rms deviation from experiment of only 0.3 eV for a test set of 33 molecules, as compared to 0.5 eV for standard INDO/S for the same set of molecules.