Ab initio calculations on the H₄ van der Waals dimer: perturbation dispersion energy versus CI treatment

Abstract

Ab initio SCF-CI calculations are performed on the (H₂)₂ dimer, including all singly and doubly-excited configurations with respect to the fundamental SCF configuration. The CI contribution to intermolecular energy is compared to the dispersion energy obtained from a perturbation treatment. Both procedures give a similar qualitative description, the CI values being slightly less attractive than the dispersion energies. The higher excitation contribution might be non-negligible in the CI treatment.