Structure and dynamics of high-pressure TIP4P water

Constant temperature molecular dynamics (N, V, T ensemble) is performed on 216 TIP4P water molecules at T=268 and 298 K and densities ρ=0.999, 1.083, and 1.149 g/cc. The main structural effect from the increase of the density is found to be, at both temperatures, weakening of tetrahedral order implied by the disappearance of the second peak in the radial distribution function. The calculated diffusion coefficient reproduces the experimentally observed anomalous behavior at T=268 K. It increases at ρ=1.083 g/cc and then decreases at ρ=1.149 g/cc. For T=298 K the diffusion coefficient decreases with increase of density, which also is in agreement with the experiment.