Prof. Christoph Dellago: The time scale problem in molecular simulations: pressure-induced structural transformations in nanocrystals
Povzetek:
The time scale problem in molecular simulations: pressure-induced structural transformations in nanocrystals
Prof. Christoph Dellago, Faculty of Physics, University of Vienna, Dunaj, Avstrija
Under suitable conditions, first-order phase transitions such as the freezing of a liquid or the structural transformation of a solid occur via a nucleation and growth mechanism, where a nucleus of the stable phase is formed in the metastable phase. The free-energy cost of creating an interface between the phases prevents this process from occurring rapidly and the transition takes place only if a fluctuation produces a sufficiently large nucleus. On a molecular time scale, the transition is a rare event and the resulting long time scales are a challenge for computer simulations. I will discuss how the transition path sampling methodology provides a framework to address this problem and to study the mechanism and the kinetics of first-order phase transitions. I will report on our work on the pressure-induced transition from the four-coordinate Wurtzite structure to the six-coordinate rocksalt structure in CdSe nanocrystals. We obtained the preferred transformation pathway and we determined the activation enthalpies and volumes, which can be directly related to experiments.
