1. Ashcroft, N. W. and Mermin, N. D. 1976.Solid State Physics, 790–795. New York: Holt, Rinehart & Winston.
2. A correspondence principle for the channelling of fast charged particles
3. Flügge, S. 1974.Practical Quantum Mechanics, Vol. 2, 150–153. New York: Springer-Verlag.
4. Kittel, C. 1963.Quantum Theory of Solids, 393New York: J. Wiley & Sons.