Instabilities of hydrogen bond network in liquid water

Abstract

A new model of the hydrogen bond network in liquid water is developed. Using the technique of polymer science, the grand canonical partition function of water is expressed by the functional integral of the field variables. The method is applied to anomalies of liquid water. Using the mean-field lattice-gas approximation it is shown that there are two instability lines, one in the supercooled region and the other in the stretched (P<0) region. Approaching the instability line in the supercooled region, the fluctuation of ice-likeness grows anomalously large and liquid water becomes unstable to be ice. Approaching the instability line in the stretched region, the fluctuation of the concentration of non-hydrogen-bonded sites grows large and liquid water becomes unstable to be gas. Divergence of the thermodynamic response functions and the mean-field values of exponents are discussed.