Molecular-Dynamics Simulation of the Phase Behavior of AgI

The phase diagram of silver iodide is simulated by the method of constant-stress molecular dynamics with use of the Parrinello-Rahman Langrangean. The β, α, rocksalt, and liquid phases are reproduced and the boundaries are similar to those observed for real AgI. The supercooled α phase and the equilibrium rocksalt phase both have diffuse fast-ion transitions and the latter cuts the rocksalt-α boundary causing it to cusp into an apparent triple point with an order-disorder transition in the α phase. This is characterized by a heat-capacity anomaly and a rise in the cation diffusion coefficient.