A metadynamics-based approach to sampling crystallisation events

We discuss the practicalities of applying the metadynamics method to sampling crystallisation events in molecular systems. Suitable choices for collective coordinates are presented along with criteria for their parameterisation. Issues arising from finite-size effects are discussed with particular reference to the generation of multiple clusters when biasing global order parameters. We also consider the applicability of two methods for enhancing the accuracy of the reconstructed free-energy landscape. The discussion is illustrated with example data from freezing in the Lennard-Jones and ice-water systems.