Atomic correlation energies. II. Converged E⁽²⁾values for Ne and Ne⁺

For pt.I see ibid., vol.11, p.1157 (1978). The second-order perturbative corrections to the Hartree-Fock ground-state energies of Ne and Ne+ are calculated using a Hartree-Fock-Roothaan approach with practically complete basis sets. The results are ENe(2)=-0.3855 au and ENe+(2)=-0.3214 au. It was found necessary to include virtual orbitals with relatively high angular momenta in the basis sets in order to saturate the E(2) values. The Ne result represents 98.8% of the empirical correlation energy. From ENe(2), ENe+(2) and the Hartree-Fock ground-state energies the authors find an ionisation potential, IPNe,calc=0.7934 au or 21.59 eV, in excellent agreement with the measured value, IPNe=21.56 eV.