Modified phonon polariton model for collective density oscillations in liquid water

Abstract

The modified phonon polariton model is proposed to quantitatively describe the dispersion of collective density oscillations of liquid water in the glass-like regime consisting of the fast and the normal sound modes. The interaction between the local electromagnetic field generated from the collective oscillations of water dipoles and the transverse collective density oscillations leads to the appearance of the two modes. This model is suitable for description of water dynamics from the Frenkel to the Debye frequency where the wavelength of the collective excitations is larger than the mean intermolecular separation at a fixed temperature and pressure. The change in some dynamical parameters of liquid water around the onset point is also pointed out, demonstrating the transformation from the hydrodynamic to the glass-like regime. The terahertz dielectric responses of liquid water are estimated and interpreted, revealing a correlation between electrodynamics and density wave. Moreover, we predict that only the high-energy mode with large wave vector could carry function of propagation of biological information. Our model might extend and apply to study collective density oscillations in the other similar liquid systems.