Molecular dynamics simulations for optical Kerr effect of TIP4P/2005 water in liquid and supercooled states.

Abstract The optical Kerr effect (OKE) spectroscopy measured with heterodyne detection (HD) is a useful tool to provide information regarding intermolecular vibrations and structural relaxations in liquid water. Recently, the measurements of the OKE spectroscopy have been extended to the supercooled regime of water. Though the measured results can be well described by using a phenomenological model, the time-resolved OKE spectroscopy of liquid and supercooled water still need a comprehensive understanding. In this paper, we investigated the OKE nuclear response functions of this peculiar liquid and their reduced spectral densities by performing molecular dynamics simulations with the TIP4P/2005 water model. The collective polarizability of water was computed via a dipolar induction scheme, which involves the intrinsic polarizability and the first-order hyperpolarizability tensor of water molecule. Our simulation results were qualitatively consistent with the HD-OKE experimental observations for displaying that the polarizability anisotropy relaxation of supercooled water in the high-density liquid phase was fragile-like by following a stretching exponential decay with an exponent β s insensitive to temperature and the temperature dependence of the relaxation time exhibited a power-law divergence at a singular temperature T s with a critical exponent γ s. Indicated by our quantitative results, T s was predominately determined by the structural arrest, but β s and γ s were not only related to the structural relaxation but also influenced by the collective polarizability of the liquid. For all investigations, the effects due to the first-order hyperpolarizability tensor were examined. Highlights • The polarizability anisotropy relaxation of high-density supercooled water was fragile-like. • The stretching exponent of the polarizability anisotropy relaxation is insensitive to temperature. • The relaxation time diverges at a singular temperature in a power law with a critical exponent. • The structural arrest is the origin for the singular temperature. • The critical exponent is related to structural relaxation and collective polarizability. [ABSTRACT FROM AUTHOR]