Exact Computation of the van der Waals Constant for Two Hydrogen Atoms

Abstract

An exact formula is obtained for $C_{\mathrm{HH}}$, the van der Waals constant which appears in $V_{\mathrm{HH}}=-\frac{C_{\mathrm{HH}}}{R^6}$, the London potential for two hydrogen atoms. Numerical evaluation gives $C_{\mathrm{HH}}=6.4990297\mathrm{}\pm 0.0000004$.