Insights into phase transitions from phase changes of clusters

The phases and phase transitions of bulk matter differ in several important ways from the phases or phase-like forms of small systems, notably atomic and molecular clusters. However, understanding those differences gives insights into the nature of bulk transitions, as well as into understanding the behaviour of the small systems. Small systems exhibit dynamic phase equilibria, large fluctuations and size-dependent behaviour in ways one cannot see with macroscopic systems. The Gibbs phase rule loses its applicability, the distinction between first-order and second-order transitions reveals a size dependence, and one can see phases in equilibrium (as minority populations) that are never the most stable thermodynamically.