1. A. Dalgarno and R. McCarroll, Proc. Roy. Soc. A237,(1956) 383.
2. M. Born and R. Oppenheimer, Annin. Phys. 84,(1927) 457.
3. M. Born and K. Huang, Dynamical Theory of Crystal Lattices, O. U. P., (1954).
4. M. Born, Nachr. Akad. Wiss., Göttingen, Mat. Phys. Kl., 1.
5. R. B. Gerber, Int. J. Quant. Chem., 11, (1967) 781.