Intramolecular correlation correction to the first-order interaction energy between H2 molecules and its influence on the H2-H2 potential surface

The intramolecular correlation correction to the first-order interaction energy between the H2 molecules has been calculated for intermolecular distances ranging from 4a0 to 8a0 and for four geometries: linear, parallel, T and crossed (non-planar). The correction is strongly anisotropic, and its contribution to the interaction energy at 6.5a0 (the region of the van der Waals minimum) varies from -4 per cent (for the T orientation) to +38 per cent - (for the linear orientation). Its isotropic component is small, ca. -6μH at 6.5a0 and shifts the isotropic part of the interaction energy, calculated as the sum of the SCF and dispersion, closer to the experimental value. (author)