Computer simulations of liquid silica: Equation of state and liquid-liquidphase transition - art. no. 011202

We conduct extensive molecular dynamics computer simulations of two models for liquid silica [the model of Woodcock, Angell and Cheeseman, J. Phys. Ch em. 65, 1565 (1976); and that of van Beest, Kramer, and van Santen, Phys. R ev. Lett. 64, 1955 (1990)] to determine their thermodynamic properties at l ow temperature T across a wide density range. We find for both models a wid e range of states in which isochores of the potential energy U are a linear function of T-3/5, as recently proposed for simple liquids [Rosenfeld and P. Tarazona, Mel. Phys. 95, 141 (1998)]. We exploit this behavior to fit an accurate equation of state to our thermodynamic data. Extrapolation of thi s equation of state to low T predicts the occurrence of a liquid-liquid pha se transition for both models. We conduct simulations in the region of the predicted phase transition, and confirm its existence by direct observation of phase separating droplets of atoms with distinct local density and coor dination environments.