Diffusion Study for α-RbAg4I5 System by Molecular Dynamics

The RbAg4I5 compound is a typical fast ion conductor. Several theoretical models for explaining this transport ion dynamic have been proposed. However, there are few studies reported on computer modeling. Herein, to study the diffusion of cation mobility, classical molecular dynamic (MD) simulations are conducted. The interstitial Ag1, Ag2, and Ag4 sites present high occupancy sites, where their activation energy is of the order of thermal energy, providing channels of high mobility. About 60.13% of the ions have a preference to occupy the Ag1 site, 27.89% for the Ag2 site with no apparent distinction for the jump between any of them, 10.26% for the Ag4 site, and a lower occupancy probability for the others, according to experimental data. Jump diffusion mechanism in alpha-RbAg4I5 is a collective phenomenon where one cation is pushed to adjacent free sites due to the close presence of other ions of the same species, following channels Ag1 -> Ag2 -> Ag1. The results of MD show advantaged paths to Ag-ion transport, which agrees with experimental data. This fact makes its study highly relevant to improve the understanding of the superionic state.