Retarded van der Waals Interactions. I. Simple Atoms

The effect of retardation on the dipole dispersion interaction between atoms has been determined. By the use of accurate frequency-dependent polarizabilities, quantitative calculations of the retardation correction to the interaction of (H, H), (H, He+), (He+, He+), (H, He), and (He, He), as well as to the three-body system (He, He, He), have been made. The procedure used was to evaluate the Casimir–Polder integral for two atoms and its three-body extension directly so as to obtain results correct for all R. Although the corrections to the limiting behavior (1 / R6 for “small” R, 1 / R7 for large R) are not large, they may be of significance for high accuracy measurements in some cases.