Journal Article interacting quantum atoms Research Support, Non-U.S. Gov't chemical bonding Bonding indices Chemical bonding MP2 Quantum Theory of Atoms in Molecules Wave function analyses atoms in molecules bimolecular nucleophilic substitution chemical reactivity conical intersections coordination number covalent energy electron delocalization electron density analysis electronic correlation energy decomposition analysis energy transfer excited states hydrogen bonding interaction energy molecular energy partitioning one-electron function partitioning quantum theory of atoms in molecules status of the methods steric repulsion water clusters