1. J. Hubbard and K. P. Jain, J. Phys. C 2, 1650 (1968).
2. J. Hubbard, Proc. R. Soc. London, Ser. A 277, 237 (1964).
3. R. O. Zaitsev, Zh. Éksp. Teor. Fiz. 112, 2223 (1997) [JETP 85, 1218 (1997)].
4. D. T. Smirnov and Yu. F. Smirnov, Theory of Optical Spectra of Transition-Metal Ions (Nauka, Moscow, 1977).
5. J. B. Goodenough, Magnetism and the Chemical Bound (Wiley, New York, 1963; Metallurgiya, Moscow, 1988).