1. C.J. Ballhausen, Introduction to Ligand Field Theory, Mc Graw-Hill, New York 1962.
2. C.E. Schäffer, Physica
114 A (1982) 28–49.
3. J.S. Griffith, Mol. Phys. 8 (1964) 217–24.
4. C.E. Schäffer and C.K. Jørgensen, Mat.-fys.Medd.Dan.Vid.Selsk. 34 no. 13 (1965) 1–20.
5. C.E. Schäffer, Pure and Applied Chemistry
24 (1970) 361–92.