1. J.H. van Vleck: Theory of Electric and Magnetic Susceptibilities (Oxford University Press, 1932) p. 1
2. K. Cho: Prog. Theor. Phys. Suppl. 106 (1991) 225
3. M. Born and K. Huang: Dynamical Theory of Crystal Lattices (Clarendon Press, 1954) Sect. 19
4. H.A. Lorentz: The Theory of Electrons (Leipzig, 1916)
5. S.I. Pekar: Zh. Eksp. Teor. Fiz. 33 (1957) 1022 [Sov. Phys. JETP 6 (1957) 785]