A perturbation theory using a local potential from Hartree–Fock orbitals

We invert a weighted average of the Fock equations to compute a local potential, which we use to form a zeroth-order local-exchange Hamiltonian for many-body perturbation theory. Convergence of the perturbation series is investigated for H2O, Be2 and Ne, and the energies to second and fourth order are consistently closer to FCI than the corresponding Møller–Plesset energies, demonstrating that non-local exchange in the zeroth-order Hamiltonian is not necessary for a convergent perturbation theory.