1. Dewar, M. J. S.: The molecular orbital theory of organic chemistry. New York: McGraw-Hill 1969
2. Bulayevsky, L. N.: JETP 51, 230 (1966)
3. Parr, R.: Quantum theory of molecular electronic structure. New York: Benjamin Press 1963
4. Lieb, E., Schultz, T., Mattis, D.: Ann. Phys. 16, 407 (1961)
5. Morozova, I. D., Dyatkina, M. E., Usp Khim. 37, 865 (1968)