Predicting crystal structures: the Parrinello-Rahman method revisited.

By suitably adapting a recent approach [A. Laio and M. Parrinello, Proc. Natl. Acad. Sci. U.S.A. 99, 12 562 (2002)]] we develop a powerful molecular dynamics method for the study of pressure-induced structural transformations. We use the edges of the simulation cell as collective variables and define a metadynamics that drives the system away from the local minimum towards a new crystal structure. In contrast to the Parrinello-Rahman method, our approach shows no hysteresis, and crystal structure transformations can occur at the equilibrium pressure. We illustrate the power of the method by studying the pressure-induced diamond to simple hexagonal phase transition in a model of silicon.