1. Ballhausen CJ (1962) Introduction to ligand field theory. McGraw Hill, New York
2. Griffith JS (1961) The theory of the transition metal ions. Cambridge University Press, Cambridge
3. Arthurs AM, Dalgarno A (1960) Proc R Soc Lond A 256:540
4. Silver BL (1976) The irreducible tensor method. Academic Press, New York
5. Piepho SB, Schatz PN (1983) Group theory in spectroscopy. Wiley, New York