Collective excitations in molten NaCl and NaI: A theoretical generalized collective modes study

A theoretical analysis of dispersion for two branches of propagating collective excitations in molten NaCl and NaI is performed using an approach of generalized collective modes. Two molten salts with different mass ratios were studied in order to clarify reported fast sound in molten NaCl [F. Demmel, S. Hosokawa, M. Lorenzen, and W.-C. Pilgrim, Phys. Rev. B 69, 012203 (2004)]. Contributions of low- and high-frequency branches to partial dynamical structure factors in molten salts are discussed.