Ab initio molecular dynamics studies of off-center displacements in CuCl

The unusual properties of CuCl have previously been interpreted using models that focus either on anharmonicity or off-center displacements from the zinc blends structure. We use nb initio molecular dynamics to show that both are important in determining the behavior of CuCl. At low temperatures, most of the Cu ions are located in off-center sites along the (111) directions. The lattice undergoes gradual transition from static to dynamic disorder with rising temperature. Increasing pressure favors the zinc blende structure, in agreement with recent Raman experiments.