Calculation of Coefficients in the Power Series Expansion of the Long-Range Dispersion Force between Atoms

Abstract

By applying an Unsöld approximation to the expression for the second‐order perturbation energy between two atoms and assuming no overlap of charge distributions, we have derived an expression for C₂n, the coefficient of the R⁻²ⁿ term in the attractive potential, in terms of C₆ and ground‐state averages of even powers of the electron—nucleus distance in the isolated atom. Values of C₈ and C₁₀ are calculated for H, He, Ne, Ar, and Kr, and estimates are made as to the accuracy of the calculations. Several comments are made on the convergence of the power series expression for the second‐order energy.