title: Communication: On the origin of the non-Arrhenius behavior in water reorientation dynamics.
abstract: We combine molecular dynamics simulations and analytic modeling to determine the origin of the non-Arrhenius temperature dependence of liquid water's reorientation and hydrogen-bond dynamics between 235 K and 350 K. We present a quantitative model connecting hydrogen-bond exchange dynamics to local structural fluctuations, measured by the asphericity of Voronoi cells associated with each water molecule. For a fixed local structure the regular Arrhenius behavior is recovered, and the global anomalous temperature dependence is demonstrated to essentially result from a continuous shift in the unimodal structure distribution upon cooling. The non-Arrhenius behavior can thus be explained without invoking an equilibrium between distinct structures. In addition, the large width of the homogeneous structural distribution is shown to cause a growing dynamical heterogeneity and a non-exponential relaxation at low temperature.
authors: Chemistry Department, Ecole Normale Supérieure, UMR ENS-CNRS-UPMC 8640, rue Lhomond, 75005 Paris, France.
authors: Guillaume
authors: G
authors: Stirnemann
authors: Damien
authors: D
authors: Laage