Atom pair partitioning of the correlation energy

Using our atomic orbital formulation of the electronic structure problem, contributions to the correlation energy are condensed over pairs of atomic centers. We show that the resulting pair energies can be used to understand how correlation energy is distributed throughout a molecule. These pair energies reflect the near-sightedness of the correlation energy while offering a simple way to represent and quantify intramolecular interactions. In particular, the dependence of these interactions with basis set is explored. We propose that strong or active interactions be treated using large basis sets while weak or inactive interactions are treated using a smaller basis set.