Many-Body Expansion of the MP2 Correlation Contribution to the Binding Energies of Water Clusters: A Localized Excitation Analysis

Abstract

The many-body expansions of Hartree–Fock (HF) and correlation contributions to water cluster MP2 binding energies converge differently: the HF contribution (one-body (1B) repulsive, two-body (2B) and three-body (3B) attractive) converges at the 3B term, whereas the MP2 correlation contribution (1B and 2B attractive) converges at the 2B term, with 99.7% arising from localized double excitations spanning one and two monomers. Two orbital excitation truncation approximations, MP2-1B2B (geometry based) and localized LMP2-1M2M (excitation space based), recover ≥99.2% of the canonical MP2 binding energies.