Nonlocal Dielectric Properties of Water: The Role of Electronic Delocalization

The nonlocal dielectric properties of liquid water are studied in the context of ab initio molecular dynamics (AIMD) simulations based on the density functional theory. We calculate the dielectric response from the charge structure factor of the liquid using the fluctuation-dissipation theorem. We show that the dielectric response function of ab initio simulations differs significantly from that of classical force-fields, both qualitatively and quantitatively. In particular, it exhibits a larger amplitude and a wider range of responding wave numbers. We suggest that the difference is due to the localization of the electronic charge density inherent in both classical force files and Wannier post-treatment of DFT densities. The localized charge models do not reproduce the shape of the response function even for q corresponding to intermolecular distances, and could lead to a significant underestimation of the dielectric response of the liquid by a factor of 10.