The helium dimer potential from a combined density functional theory and symmetry-adapted perturbation theory approach using an exact exchange-correlation potential

Starting with an analytic representation of the electron density from a Hylleraas wavefunction we have obtained an analytic representation of the exchange - correlation potential of the helium atom. This, essentially exact, exchange - correlation potential has been employed to test a recently developed approach, named DFT-SAPT, which combines symmetry-adapted perturbation theory of intermolecular interaction energies with a density functional theory description of the interacting monomers. In DFT-SAPT all of the second-order contributions including the exchange corrections are determined from coupled-perturbed density functional theory. Comparison of the results for the helium dimer to previous high-quality supermolecular and intermolecular perturbation theory results demonstrates the success of the new approach.