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

It is investigated to which extent the effect of intramolecular electron correlation on intermolecular first-order Coulomb and exchange energies can be accounted for when solely the reference determinant of the Brueckner coupled-cluster-doubles scheme is used to construct the charge density and the density matrices of the monomers. Considering the dimers He2, Ne2, Ar2, NeAr, NeHF, ArHF, (H2)2, (HF)2, and (H2O)2 the Brueckner orbital approximation in general is found to improve considerably upon the results of the Hartree–Fock determinant.