THE NONADDITIVE EXCHANGE ENERGIES OF H-3 AND HE-3

Non-additive SCF energies are calculated for H3 (quartet spin state) and He3 using Hartree-Fock quality basis sets containing only s functions. The results are analysed using a modification of an effective Gaussian model, replacing the explicit dependence on Gaussians by related dimer and/or trimer properties. A good fit to the SCF results is obtained using a model based on dimer and trimer charge density overlap integrals, and two adjustable parameters.