Mechanism of the pressure-induced wurtzite to rocksalt transition of CdSe

The transformation of cadmium selenide from the wurtzite type (B4) structure to its high-pressure phase (rocksalt type structure, B1) is investigated by means of molecular dynamics simulations using a recently introduced transition path sampling approach. This allows a very detailed mechanistic analysis, which is not spoiled by driving the process kinetics by excessive pressure. Furthermore, our approach is free of predefining a model reaction coordinate and the "true" reaction coordinate is derived as a direct result from the simulations instead. Starting the calculation from mechanistically different transition paths, we are able to identify a single favored mechanism for the transformation. The phase transition occurs by nucleation of a slab and subsequent phase growth. The underlying mechanism is identified as a shearing of (110) layers. This layer shuffling may occur in two equivalent ways-parallel and antiparallel-which in average are observed to occur at equal probability.