1. T. Szondy, Acta Phys. Hung.,17, 303, 1964.
2. G. G. Hall, Phil. Mag. (8),6, 249, 1961.
3. G. G. Hall, Accuracy of Calculated Atomic and Molecular Properties. [Advances in Quantum Chemistry, Vol. 1. (Edited by Per-Olov Löwdin.) Academic Press, New York-London, 1964.]
4. E. Kapuy, to be published in J. Chem. Phys.
5. An excellent survey of this question has been given byH. Preuss in Fortschritte der Physik,10, 271, 1962.