The Hermiticity of the dynamical matrix

In the usual calculation of the dynamical matrices of a crystal the self terms can give rise to non-Hermitian dynamical matrices, particularly when the crystal symmetry is low. It has been suggested that Hermiticity be imposed upon the interatomic force constants as an extra condition. It is shown that this is not necessary and that, with a correct treatment of the basic equations of lattice dynamics, the dynamical matrices will automatically be Hermitian.