CORRELATED POLARIZATION PROPAGATOR CALCULATIONS OF STATIC POLARIZABILITIES

We present a systematic comparison of the correlation contribution at the level of the second-order polarization propagator approximation (S OPPA) and MP2 to the static dipole polarizability of (1) Be, BeH-, BH. CH+, MgH-, AlH, SiH+, and GeH+; (2) BH3, CH4, NH3, H2O, HF, BF, and F 2; and (3) N2, CO, CN , HCN, C2H2, and HCHO. Fairly extended basis set s were used in the calculations. We find that the agreement with exper imental values is improved in SOPPA and MP2 over the results at the SC F level. The signs and magnitudes of the correlation contribution in S OPPA are similar to those obtained in analytical derivative MP2 calcul ations. However, it is not possible to say, in general, which method g ives the largest correlation contribution or the best agreement with e xperiment, nor is it possible to make a priori prediction of the sign of the correlation contribution. For the first group of molecules, whi ch have a quasi-degenerate ground state, additional CCDPPA and CCSDPPA calculations were performed and compared with polarizabilities obtain ed as analytical/numerical derivatives of the CCD and CCSD energies. T he CCSDPPA results were found to be in better agreement with other cal culations than were the SOPPA results, demonstrating the necessity of using methods based on infinite-order perturbation theory for these sy stems. (C) 1994 John Wiley & Sons, Inc.