Atomistic mechanisms for wurtzite-to-rocksalt structural transformation in cadmium selenide under pressure

The pressure-induced structural transformation in cadmium selenide is studied with the isothermal-isobaric molecular-dynamics method and electronic-structure calculations based on the density-functional theory. The reversible transformation between the fourfold-coordinated wurtzite structure and the sixfold-coordinated rock-salt structure is successfully reproduced in the molecular-dynamics simulations, in which atomistic transition mechanisms including the existence of a metastable state as well as barrier states along the transition paths are observed. Accurate density-functional calculations confirm these transition paths. It is shown that there are at least three transition paths, which are characterized by atomic shifts in the (0001) plane of the wurtzite structure. The energy barrier for the transformation is found to be about 0.13 eV/pair and is almost independent of the paths.