1. Cf. the contributions of R. F. Bader (p. 15), R. Daudel (p. 3) and J. P. Malrieu (p. 9) in Volume 1 of the present book.
2. Lennard Jones, J. E.: Proc. Roy. Soc. (London) A198, 114 (1949);
3. Hall, G.G. and Lennard Jones, J. E.: ibid. A202, 155 (1950);
4. Boys, S. F.: in Quantum Theory of Atoms, Molecules and Solid State (ed. by P. O. Löwdin ), New York, Academic Press (1966).
5. Edmiston, E. and Ruedenberg, K.: Rev Med. Phys. 34, 457 (1963).