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2. See for instance the volume: Heterojunction Band Discontinuities, edited by F. Capasso and G. Margaritondo ( North-Holland, Amsterdam, 1987 ).
3. L. Kleinman Phys. Rev. B 24, 7412 (1981).
4. R. Resta, S. Baroni, and A. Baldereschi, Superlattices and Microstr. 5, X XXX (1989)
5. S. Baroni, R. Resta, and A. Baldereschi. Proc. 19
th
Int. Conf. on THE PHYSICS OF SEMICONDUCTORS, edited by W. Zawadzki ( Institute of Physics, Polish Academy of Sciences, Wroclaw, 1988 ), p. 525.