title: An Examination of Basis Set Superposition Error at the Correlated Level:  Illuminating the Role of the Exchange Repulsion.
abstract: A reformulated 'virtuals-only' counterpoise procedure for the correction of basis set superposition error is introduced and applied to an examination of the interaction energy of the helium dimer. This method allows a direct calculation of the exchange (Pauli) repulsion at the correlated level. Our findings suggest that at the correlated level the Pauli repulsion may be interpreted as a decrease in the monomer correlation energy calculated using the dimer virtual space relative to that with a monomer-only virtual space. This observation provides further theoretical justification for the Full Counterpoise procedure in preference to any virtuals-only counterpoise procedure.
authors.affiliation: Department of Chemistry and Physics, University of New England, 11 Hills Beach Road, Biddeford, Maine 04005.
authors.forename: Clinton S
authors.initials: CS
authors.lastname: Nash