Charge effects in the structure of an almost-ionic solid: Molecular-dynamics studies

The molecular-dynamics studies reported in this work concern the behavior of a system, with a pair-potential model appropriate for CuI, as a function of its charge {}Z{}. These studies are carried out at two temperatures. The lower at T=625 K, corresponds to its {γ} phase; the higher, at T=700 K, to its {α} phase. The structure of the system in the {γ} phase at {}Z{}=0.6 is zinc-blende. When the charge is lowered to {}Z{}=0.3 the system is found in a rocksalt structure. At {}Z{}=0.2 the structure is still rocksalt, but the cations now diffuse through hopping. At {}Z{}=0 it is found in the molten state. In the {α} phase, at {}Z{}=0.6, the system is superionic with the anions sitting on a fcc sublattice while the cations exhibit a liquidlike structure. For {}Z{}=0.2, the system is found in a rocksalt structure, and is no longer superionic. When the charge is completely removed the system is again found in the molten state. The lowering of the charge in this model almost-ionic solid appears to exhibit effects akin to those found by increasing its pressure.