Accurate Analytical He-He van der Waals Potential Based on Perturbation Theory

A simple analytical expression for the entire van der Waals potential curve of the helium dimer is derived from perturbation theory. The repulsive part is essentially from Duman and Smirnov [Opt. Spectrosc. 29, 229 (1970)] who assume the exchange of only one pair of electrons at any one time. The potential depends only on the known dispersion coefficients and the amplitude of the asymptotic wave function and the ionization energy of the atoms. Without any adjustable parameters the potential is in excellent agreement with the latest experimental and theoretical results and predicts the existence of the He dimer. The same method can be applied to heavier rare gases.