Non-Hermitian dynamical matrices in the dynamics of low symmetry crystals

Abstract

It is shown that in the Born-von Kármán theory of lattice dynamics the dynamical matrix may, under particular conditions, be non-hermitian for low symmetry crystals. Normal modes can then be introduced by using both right and left eigenvectors of the matrix. The hermitian character of the matrix can be maintained by imposing constraints on the interatomic force constants.