Static and dynamic properties of stretched water

We present the results of molecular dynamics simulations of the extended si mple point charge model of water to investigate the thermodynamic and dynam ic properties of stretched and supercooled water. We locate the liquid-gas spinodal, and confirm that the spinodal pressure increases monotonically wi th T, supporting thermodynamic scenarios for the phase behavior of supercoo led water involving a "non-reentrant" spinodal. The dynamics at negative pr essure show a minimum in the diffusion constant D when the density is decre ased at constant temperature, complementary to the known maximum of D at hi gher pressures. We locate the loci of minima of D relative to the spinodal, showing that the locus is inside the thermodynamically metastable regions of the phase diagram. These dynamical results reflect the initial enhanceme nt and subsequent breakdown of the tetrahedral structure and of the hydroge n bond network as the density decreases. (C) 2001 American Institute of Phy sics.