First-order intermolecular interaction energies from Kohn–Sham orbitals

It is investigated whether similar to Brueckner orbitals also Kohn–Sham monomer orbitals from current density functional approaches reliably reproduce electron correlation effects on first-order Coulomb and exchange dimer interaction energies. While the Coulomb energy is potentially exact, i.e., exact, if the monomers exact exchange-correlation potential were known, this is not true for the exchange interaction energy. Considering He2, Ne2, Ar2, NeAr, NeHF, ArHF, (H2)2, (HF)2, and (H2O)2 it is nevertheless found that electron correlation effects on both Coulomb and exchange energies were accurately reproduced when the orbitals were determined with the newly developed asymptotically correct exchange-correlation potential PBE0AC.