We propose an extension of the van der Waals equation which is designed to incorporate, in an approximate fashion, the effects of the network of hydrogen bonds that exist in liquid water. The resulting model qualitatively predicts the unique thermodynamic properties of water, including those of the deeply supercooled states. It also reconciles two proposals for the phase behavior of supercooled and stretched water and provides a thermodynamic origin for the observed polymorphism of the amorphous solid form of water.

• Received 28 April 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.1632