Nucleation: Free energy of small clusters

Recent theoretical developments of crystal nucleation are critically review ed with the emphasis placed on modelling the properties of small clusters. Predictions for the size and temperature dependence of the interfacial free energy by phenomenological and density-functional theories are discussed i n the light of experiments and computer simulations. Various models suggest an absolute instability of the undercooled liquid far below the melting po int and of the superheated crystal far above the melting point. The experim ents and computer simulations are consistent with this picture.