CHARACTERIZATION OF THE RANDOM PHASE APPROXIMATION WITH THE INTERMEDIATE NEGLECT OF DIFFERENTIAL-OVERLAP HAMILTONIAN FOR ELECTRONIC SPECTROSCOPY

The random phase approximation (RPA) in conjunction with the intermediate neglect of differential overlap method for spectroscopy (INDO/S) is demonstrated to give accurate transition energies for electronic excitations. The RPA guarantees formal equivalence between calculated oscillator strengths in the dipole length and velocity form. Although this provision is only true for a complete basis, considerable improvement is noticed in the prediction of oscillator strengths in comparison with experiment and between oscillator strengths calculated by using the dipole length and dipole velocity formalisms. A comparison is made between the RPA and the more familiar singles configuration interaction (CIS) method for spectroscopy for benzene, pyridine, and the diazines and for extended systems consisting of many fused benzene rings.