Dipole-phonon coupling and dielectric relaxation

Equations of motion for the average polarisation are derived from a microscopic approach by use of the local density matrix. A specific form of the dipole-phonon coupling in the memory kernel is investigated and the necessary conditions for the generation of a non-Debye form of response examined. It is shown that these conditions can only be fulfilled by allowing for dipole-induced distortion with the lifetime of the “phonons” determined by the lifetime of the dipole correlation.