Dynamics of simulated water under pressure

We present molecular dynamics simulations of the extended simple-point-char ge model of water to probe the dynamic properties at temperatures from 350 K down to 190 K and pressures from 2.5 GPa (25 kbar) down to -300 MPa (-3 k bar). We compare our results with those obtained experimentally, both of wh ich show a diffusivity maximum as a function of pressure. We find that our simulation results are consistent with the predictions of the mode-coupling theory for the dynamics of weakly supercooled liquids-strongly supporting the hypothesis that the apparent divergences of dynamic properties observed experimentally may be independent of a possible thermodynamic singularity at low temperature. The dramatic change in water's dynamic and structural p roperties as a function of pressure allows us to confirm the predictions of MCT over a much broader range of the von Schweidler exponent values than h as been studied for simple atomic liquids. We also show how structural chan ges are reflected in the wave-vector dependence of dynamic properties of th e liquid along a path of nearly constant diffusivity. For temperatures belo w the crossover temperature of MCT (where the predictions of MCT are expect ed to fail), we find tentative evidence for a crossover of the temperature dependence of the diffusivity from power-law to Arrhenius behavior, with an activation energy typical of a strong liquid. [S1063-651X(99)11712-4].