First-order intermolecular interaction energies from coupled-cluster Brueckner orbitals

It is investigated to which extent the effect of intramolecular electron co rrelation on intermolecular first-order Coulomb and exchange energies can b e accounted for when solely the reference determinant of the Brueckner coup led-cluster-doubles scheme is used to construct the charge density and the density matrices of the monomers. Considering the dimers He-2, Ne-2, Ar-2, NeAr, NeHF, ArHF, (H-2)(2), (HF)(2), and (H2O)(2) the Brueckner orbital app roximation in general is found to improve considerably upon the results of the Hartree-Fock determinant. (C) 2000 American Institute of Physics. [S002 1-9606(00)30816-9].