Spectral signatures of the diffusional anomaly in water

Abstract

Power spectra for various tagged particle quantities in bulk extended simple point charge model water [ H. J. C. Berendsen, J. R. Grigera, and T. P. Straatsma, J. Phys. Chem. 91, 6269 (1987) ] are shown to have a regime with 1/f^α dependence on frequency f with a lying between 1 and 1.5 if the dynamical changes in the particular observable are sensitive to the multiple time-scale behavior of the hydrogen-bond network. The variations in mobility associated with the diffusional anomaly are mirrored in the scaling exponent a associated with this multiple time-scale behavior, suggesting that monitoring of 1/f^α behavior is a simple and direct method for linking phenomena on three distinctive length and time scales: the local molecular environment, hydrogen-bond network reorganizations, and the diffusivity. Our results indicate that experimental studies of supercooled water to probe the density dependence of 1/f^α spectral features, or equivalent stretched exponential behavior in time-correlation functions, will be of interest.