Vibrational Modes of Disordered Linear Chains

Abstract
The kth normal mode of vibration (i.e., the atomic displacements) of a disordered one‐dimensional lattice (masses and force constants completely arbitrary) with nearest‐neighbor interaction has precisely k − 1 nodes. A fortiori, the same is true for ordered one‐dimensional lattices with any number of atoms per unit cell. This theorem exhibits a close relationship between eigenfunctions in monatomic ordered lattices (to which its application has been known for many years) and disordered lattices; a relationship which appears surprising in view of recent demonstrations of the gross differences exhibited in the distribution of eigenvalues. It is thus suggested that some basic concepts of ordered lattice dynamics—propagation vector, phonon momentum, etc.—may retain some simple validity for disordered solids as well. Some numerical examples are given.

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