Sampling in the Multicanonical Ensemble: Small He Clusters in W

We carry out generalized-ensemble molecular dynamics simulations of the formation of small helium (He) clusters in bulk tungsten (W), a process of practical relevance for fusion energy production. We calculate formation free energies of small helium clusters at temperatures up to the melting point of W, encompassing the whole range of interest for fusion-energy production. From this, parameters like cluster break-up or formation rates can be calculated, which help to refine models of microstructure evolution in He-irradiated tungsten.