An exact solution of the van der Waals interaction between two ground-state hydrogen atoms. II

Systematic refinement and extension are presented for the momentum space approach proposed previously to the H(1s)–H(1s) van der Waals interaction. The results are applied to the solution of the first order perturbation equation in its Schrödinger form and almost exact perturbation wave functions are determined up to the order of R−5 where R is the internuclear distance. Using these functions, highly accurate values of the dipole–quadrupole, quadrupole–quadrupole, and dipole–octupole interaction energies are obtained in an extremely simple manner.