Second-order optical properties and van der Waals coefficients of atoms and molecules in the random phase approximation

Abstract

An RPA calculation and a direct sum over states is used to calculate second-order optical properties and van der Waals coefficients. A basis set expansion technique is used and no continuum-like functions are included in the basis. However, unlike other methods we do not force the basis functions to satisfy any sum-rule constraints but rather the formalism (RPA) is such that the Thomas-Reiche-Kuhn sum rule is satisfied exactly. Central attention is paid to the dynamic polarizability from which most of the other properties are derived. Sample results are shown for helium and molecular hydrogen. Agreement with experiment and other theoretical approaches is good and the practicality of our method suggests its application to larger molecular systems and other properties.

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