A comparison of semi-local and non-local pseudo-potential techniques: calculations on Fe and FeH+

A new parameterization scheme is proposed for valence electron calculations which employ the pseudopotential formalism. This scheme has been implemented in calculations for Fe, Fe⁺, Fe²⁺, Fe³⁺ and FeH⁺. In comparison with conventional all-electron calculations the errors are of the order of 1 per cent in valence orbital energies, 0·5 per cent in ionization energies and 2 per cent in the molecular binding energy. Detailed comparisons are made between the present method, which is formulated in terms of orbital projection operators, and recent calculations based on local, angular momentum dependent, effective potentials. The two approaches are found to be capable of almost equal accuracy.