(456a) Role of Bond Flexibility On the Diffusion and Shear Viscosity of Water

Molecular dynamics simulations for the shear viscosity and self diffusion coefficient of pure water were performed to investigate the effect of including intramolecular degrees of freedom in simple point charge (SPC) models over a wide range of state points. Results are reported for the flexible SPC/Fw model, its rigid SPC counterpart, and the widely used SPC/E model. The simulations covered the liquid phase at 277.15 K and 353.15 K and the supercritical phase at 673.15 K and pressures up to 200 MPa. The flexibility exhibited by the SPC/Fw model results in slowing down of the dynamics. That is, it results in higher shear viscosities and lower diffusion coefficients than can be obtained from the SPC model, and with this in better agreement with experimental data. Significantly, the SPC/Fw model can be used to adequately predict the diffusion coefficients at ambient and supercritical temperatures over a wide range of pressures. In the ambient temperature range, the simulation results for the shear viscosity by SPC/Fw are superior to those of the conventional rigid bond models.