CORRELATED DIPOLE OSCILLATOR SUM-RULES

The second order polarization propagator approximation (SOPPA) has bee n applied to the calculation of the dynamic dipole polarizability, alp ha(omega), of the molecules N-2, C2H2, CO, and HCN. The dipole oscilla tor sum rules S(-4) and S(-6), which are the leading contributions to the Cauchy expansion of the polarizability, have also been evaluated a t SOPPA level, using a polynomial fit to this expansion. These are the first reported values of the higher sum rules obtained using the SOPP A approach, and we observe excellent agreement with experiment. We als o discuss the applicability of scaling or additivity expressions for o btaining the correlated polarizability from static correlated and dyna mic uncorrelated quantities.