Propagating Collective Excitations in Molten Salts

Abstract

Longitudinal as well as transverse dynamics of a molten salt beyond the hydrodynamic region is studied within the generalized collective modes (GCM) approach. An analytical three-variable model is applied to the treatment of the coupled long-and short-time charge fluctuations. Dispersion laws of propagating kinetic collective excitations such as optic phonon-like modes, heat and shear waves are obtained and analyzed for the case of molten NaCl within the eight-variable GCM scheme, combining the analytical methods and molecular dynamics simulations.

Nonhydrodynamic collective processes in molten salts: Theory and ab initio simulations

“…On the next step one can estimate the changes in the dispersion of collective modes caused by the coupling effects with some relaxation processes. Such a scheme was successfully applied in a study of structural relaxation in pure liquids 14, where the coupling of the nonhydrodynamic structural relaxation process with the “bare” hydrodynamic sound mode led to a “positive dispersion” of the sound branch. For the case of molten salts the “bare” collective modes are of special interest, because namely the “bare” frequencies of longitudinal (LO) and transverse (TO) optic modes should enter a sum rule for ionic melts 15, which corresponds to the Lyddane–Sachs–Teller relation known for ionic crystals 16.…”