Vibrational density of states and homogeneous linewidth in molecular crystals: Many-phonon processes in nitrogen

This paper summarizes, simplifies, and extends some recent developments in the theory of phonon damping in anharmonic crystals. We propose an approach in which the damping is described in terms of two ingredients:m(1) a computed or estimated one-phonon density of states, and (2) average anharmonic couplings between the phonons, fitted to the experimental temperature dependence of the phonon damping. Solid nitrogen is chosen as a test case and the coupling coefficients obtained from the fit are correlated to the three-, four-, and five-phonon couplings computed from a potential model.