On decomposition of second-order Mo/ller–Plesset supermolecular interaction energy and basis set effects

The basis set effects on the total self-consistent field (SCF) and second-order Mo/ller–Plesset (MP2) interaction energies in the HF dimer (in the equilibrium geometry) are investigated in relation to their components: electrostatic, exchange, induction, and dispersion, calculated within the framework of intermolecular Mo/ller–Plesset perturbation theory (IMPPT). The basis set dependence of the SCF interaction energy in the HF dimer is almost exactly determined by the electrostatic contribution. The exchange, induction, and the SCF-deformation terms are found substantially less sensitive. The MP2 correlation contribution reflects primarily the basis set dependence of dispersion. However, an accurate image of the basis set dependence is reproduced only if the electrostatic-correlation term is considered as well. Other correlation contributions: the deformation- correlation and exchange terms are found to be much less sensitive to basis set effects. All these conclusions are valid only under the condition that the supermolecular interaction energies are counterpoise-corrected for the basis set superposition error and IMPPT interaction energies are calculated with the full basis set of the dimer.