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

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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.