Transport coefficients of the TIP4P-2005 water model

A detailed understanding of the dynamics of liquid water at molecular level is of fundamental importance as well as have applications in many branches of science and technology. In this work, the diffusion of the TIP4P-2005 model of water is systematically investigated in liquid phase in the temperature range 210-310 K. The translational and rotational diffusions, as well as correlations between them, are examined. The effects of system size and shape are also probed in this study. The results suggest the presence of a temperature of dynamical arrest of molecular translations in the range of 150-180 K and of molecular rotations in the range of 80-130 K, depending on specific direction. A substantial change in the preferred directions of translations and rotations relative to the molecular coordinate system is observed slightly below (approximate to 15 K) the melting temperature of the model. It is shown that there is a correlation between translational and rotational molecular motions essential for diffusion in the liquid. The presence of hydrodynamic size effects is confirmed and quantified; it is also shown that using a non-cubic simulation box for a liquid system leads to an anisotropic splitting in the diffusion tensor. The findings of this study enhance our general understanding of models of water, specifically the TIP4P-2005 model, as well as provide evidences of the direct connection between thermodynamics of liquid water and dynamics of its molecules. (C) 2012 American Institute of Physics. [doi:10.1063/1.3677196]