Polar nanoregions in water: A study of the dielectric properties of TIP4P/2005, TIP4P/2005f and TTM3F

We present a critical comparison of the dielectric properties of three models of water - TIP4P/2005, TIP4P/2005f, and TTM3F. Dipole spatial correlation is measured using the distance dependent Kirkwood function along with one-dimensional and two-dimensional dipole correlation functions. We find that the introduction of flexibility alone does not significantly affect dipole correlation and only affects ε(ω) at high frequencies. By contrast the introduction of polarizability increases dipole correlation and yields a more accurate ε(ω). Additionally, the introduction of polarizability creates temperature dependence in the dipole moment even at fixed density, yielding a more accurate value for dε/dT compared to non-polarizable models. To better understand the physical origin of the dielectric properties of water we make analogies to the physics of polar nanoregions in relaxor ferroelectric materials. We show that ε(ω, T) and τ_D(T) for water have striking similarities with relaxor ferroelectrics, a class of materials characterized by large frequency dispersion in ε(ω, T), Vogel-Fulcher-Tammann behaviour in τ_D(T), and the existence of polar nanoregions.