From four- to six-coordinated silica: Transformation pathways from metadynamics

We study transformation pathways leading from 4- to 6-coordinated silica using an improved version of the metadynamics method for the study of structural phase transitions in crystals [Martonak, Laio, and Parrinello, Phys. Rev. Lett. 90, 075503 (2003)]. The technique is able to simulate complex reconstructive structural transformations proceeding via number of intermediate states. In particular, we reproduce the experimentally observed crystal structures that are found upon pressurization of alpha-quartz. We also predict a low-energy transformation pathway from coesite to the metastable alpha-PbO2 phase.