The effect of intermolecular interactions on the electric properties of helium and argon.: I.: Ab initio calculation of the interaction induced polarizability and hyperpolarizability in He2 and Ar2

The frequency-dependent interaction induced polarizabilities and second hyperpolarizabilities are calculated for He-2 at the coupled cluster singles and doubles and full configuration interaction levels and for Ar-2 at the coupled cluster singles and doubles level. The frequency-dependence is approximated by a power series to second-order in the frequency arguments using Cauchy moments and hyperpolarizability dispersion coefficients. Using large correlation consistent basis sets, results close to the basis set limit are obtained. The computed curves for the interaction induced (hyper-) polarizabilities are tabulated for a range of internuclear distances. The data are employed in a companion paper to make for the first time a direct comparison between the experimentally determined pressure dependence of an ESHG hyperpolarizability and ab initio calculated hyperpolarizability second virial coefficients. (C) 1999 American Institute of Physics. [S0021-9606(99)31146-6].