Correlation of Static and Dynamic Heterogeneities in Supercooled Water by Means of Molecular Dynamics Simulations

Abstract

Abstract The unusual increase of diffusivity of supercooled water upon compression seems to be related to the existence of at least two major distinct local structural forms: a "low-density" structure, exhibiting an almost perfect tetrahedral hydrogen bonding network, and a "high-density" structure, characterized by defects in this network. The structural changes can be measured by the "tetrahedricity parameter", describing the deviation from the ideal tetrahedron. In this paper we show that the anomalous diffusion behavior upon compression cannot only be related to the structural heterogeneities but also to dynamical heterogeneities occuring in supercooled liquid water. This is shown for translational heterogeneities which decrease with temperature and pressure. Both, static and dynamic heterogeneities can be correlated. They are substantial at low temperatures and moderate pressures and diminish with increasing temperature and pressure, respectively. Our results are based on molecular dynamics simulations of the TIP4P-Ew water model [1].