Long‐Range Interaction of Helium Atoms. B. Study of Approximations

Abstract

The higher‐order corrections to the calculations of the intermolecular force by the many‐electron theory of atoms and molecules are studied and those involving two‐electron effects are found to be small. In particular, the corrections to the coefficient of R⁻⁶ due to normalization are about 2%. Allowing interatomic pair functions to couple with one another leads to an error of −3.4%. Including all of these effects the coefficient of R⁻⁶ is −1.363 in atomic units. The currently accepted value is −1.47. A very approximate study of three‐electron correlations in the wavefunction suggests that these may contribute substantially and bring about agreement between the two values.