Orientational relaxation in molecular solids with translation rotation coupling

Abstract

Starting from a Hamiltonian with bilinear coupling of translations and rotations and with single-particle orientational potential, we derive a closed transport equation for the dynamic displacement–displacement correlation function. The coupling to the rotation leads to a softening of the phonons and to an instability in the lattice at the orientational phase transition. The memory kernel which is due to the orientational velocity correlations is calculated in a systematic and consistent way. This leads to additional resonances in the displacement–displacement correlation function.