A simple analytical model of water

Water is an unusual liquid. It expands upon freezing, has minima in its volume, heat capacity, and isothermal compressibility with temperature, and shows signs of a first-order phase transition when supercooled. These anomalies disappear at high pressures. We review a recent analytical theory that predicts water's thermal properties and the main features of its phase diagram, including multiple crystalline phases and a fluid-fluid transition in the supercooled liquid. It also predicts a fragile-to-strong crossover in supercooled water's temperature-dependent relaxation processes. The theory is based on a simplified model for how triplets of waters interact via hydrogen bonds, steric repulsions, and dispersion attractions. It is designed to give simple insights into the microscopic origins of water's properties. (C) 2003 Elsevier Science B.V. All rights reserved.