Freezing, melting, spinodals, and clusters

A simple theory for melting, freezing, and phase coexistence is presented with emphasis on the relation between small clusters and spinodal behavior. This theory, coupled with the results of computer simulations, suggests a reinterpretation of spinodals and first-order phase changes. We find sufficient conditions for a system of mutually attracting quasiparticles to exhibit the characteristic ‘‘S-bend’’ found, e.g., for subcritical isotherms of a van der Waals fluid, and discuss how the theory may be extended explicitly to finite clusters.