Freezing: Density Functional Theory

Abstract

At fixed pressure, as the temperature is decreased all liquids freeze. [Liquid helium at pressures below about 25 atm appears to be the only exception!] Why do liquids abandoned their random, ‘disordered’ structure, and form periodic arrays? As surprising as it seems, at present there is no molecular level, first principles theory of freezing or melting, even for the simplest materials. The prediction of phase diagrams is an important first step in understanding the crystal/melt interface, crystallization near equilibrium, and nucleation. Recently a new approximate theory for the freezing of classical liquids, known as the density functional (DF) theory, has been developed.¹ The mathematical structure of the theory is simple enough that it provides an attractive starting point for theories of more complex, dynamical phenomena.