1. I.M. Lifshits: J. Phys. USSR 7, 215, 249 (1943); J. Phys. USSR 8, 89 (1948)
2. W. Ludwig: Ergebnisse der Exakten Naturwiss. Vol. 35 (Springer, Berlin, Göttingen, Heidelberg 1964)
3. W. Ludwig: “Recent Developments in Lattice Theory”, in Springer Tracts in Modern Physics, Vol. 43 (Springer, Berlin, Heidelberg, New York 1967)
4. A.A. Maradudin: “Theoretical and Experimental Aspects of the Effects of Point Defects and Disorder on the Vibrations of Crystals”, in Solid State Physics Vol. 18, 273, Vol. 19, 1 (Academic Press, New York 1966)
5. A.A. Maradudin, E.W. Montroll, G.H. Weiss, I.P. Ipatova: “Theory of Lattice Dynamics in the Harmonic Approximation”, in Solid State Physics, Suppl. 3, 2nd ed. (Academic Press, New York 1971)