Dynamical structure factor ofα-AgI

Abstract

Dynamical structure factors of the superionic conductor \ensuremath{\alpha}-AgI are calculated with a molecular-dynamics method. The interionic potential is assumed to consist of the Coulomb and the soft-core potentials. Correlated motions of mobile and immobile ions are investigated by partial dynamical structure factors and the spectra of the velocity-autocorrelation functions. The transverse modes are also examined by both the dynamical structure factors and the transverse-current-correlation functions. It is clarified that the vibrational motions of cations and anions are strongly correlated in the longitudinal-acoustic mode at long wavelengths. The motion of cations, however, has no correlation with the longitudinal-optic mode of the anion sublattice for larger wave vectors. The frequency of the transverse vibration of cations is lower than that of anions, which shows that the transverse motions of cations and anions do not occur in phase. Summarizing these results, the mechanism of the diffusion is presented from a dynamical viewpoint.