Molecular dynamics studies of molten NaI II. Mass-, charge- and number-density fluctuations

Molecular dynamics simulations of molten NaI have been performed using both rigid-ion and polarizable-ion models. The mass-, charge- and number-density autocorrelation functions have been calculated together with their frequency spectra. The liquid-state analogues of longitudinal optic and acoustic phonons are identified at longer wavelengths. The acoustic modes are weak and broad. The major differences between the rigid-ion model and the polarizable-ion model are that(1) there is a substantial difference between their static charge—charge structure factors, SQQ(q), and(2) the normalized charge-charge dynamical structure spectra at longer wavelengths differ in intensity and frequency of the optic mode. The mode for the polarizable-ion model occurs at a lower frequency and is less well resolved.