1. Scherr C. W., Sanders F. C., Knight R. E.,in: Perturbation Theory and its Applications in Quantum Mechanics, (ed. C. H. Wilcox), John Wiley and Sons Inc., New York 1966, p. 97;
2. also:Ashamar K., Lyslo G., Midtdal J., J. Chem. Phys.60 (1974), 3403 and references thereof.
3. Hirschfelder J. O., Brown W. B., Epstein T. S., Advan. Quant Chem.1 (1964), 345;
4. Horák Z. J., Modern Quantum Chem.2 (1965), 7.
5. Knight R. E., Phys. Rev.183 (1969), 45, also see references in [7].