Ab initio study of dispersion of optic-like modes in a molten salt: Effect of ion polarization

Longitudinal and transverse dynamics of molten NaCl beyond the hydrodynamic region is studied by generalized collective modes (GCM) analysis of relevant time correlation functions obtained in ab initio molecular dynamics. A comparison with results of rigid-ion treatment of collective dynamics in the molten salt is made. A reduction of the long-wavelength gap between longitudinal and transverse optic-like excitations due to polarization effects is discussed. We propose an analysis, based on analytical expressions for ‘bare’ propagating collective excitations, that are a generalization of Takeno–Goda formulae for the case of binary disordered system at arbitrary wavenumber.