CI-Hylleraas variational calculation on the ground state of the neon atom

This calculation demonstrates that the combined configuration-interaction-Hylleraas (CI-Hy) variational method of Sims and Hagstrom can be applied to the ¹S ground state of the neon atom. Coordinates rᵢⱼ have been included in the wave function so as to correlate explicitly the motion of all pairs of electrons in the atom. An energy of - 128.8298 hartree has been obtained from an 83-term wave function (73.5% of the correlation energy). An analysis of the pair correlation energies shows that it is more difficult to represent the electronic correlation in p-p and s-p pairs than s-s pairs using Hylleraas functions. More experience with CI-Hy calculations on atoms containing as many as ten electrons is required before the method can compete with and give higher accuracy than the conventional CI calculations.