Description of the dispersion term between two molecules and two atoms from an ab initio perturbative procedure: H2 + H2 and Ne + Ne

Abstract

From the examples of two hydrogen molecules and two neon atoms we have tried to show some of the characteristics of the dispersion term in an ab initio perturbation procedure; for example, the importance of different partitionings of the molecular Hamiltonian, the need for diffuse polarization functions, the rather good agreement between the Hartree-Fock dispersion term and the semiempirical results using the multipole expansion, and the importance of certain molecular orbitals.