Electronic Polarizability and the Effective Pair Potentials of Water

Employing the continuum dielectric model for electronic polarizability, we have developed a new consistent procedure for parametrization of the effective nonpolarizable potential of liquid water. The model explains the striking difference between the value of water dipole moment mu approximate to 3D reported in recent ab initio and experimental studies with the value mu(eff) approximate to 2.3D typically used in the empirical potentials, such as TIP3P or SPC/E. It is shown that the consistency of the parametrization scheme can be achieved if the magnitude of the effective dipole of water is understood as a scaled value mu(eff) = mu/root epsilon(el), where epsilon(el) = 1.78 is the electronic (high-frequency) dielectric constant of water, and a new electronic polarization energy term, missing in the previous theories, is included. The new term is evaluated by using Kirkwood-Onsager theory. The new scheme is fully consistent with experimental data on enthalpy of vaporization, density, diffusion coefficient, and static dielectric constant. The new theoretical framework provides important insights into the nature of the effective parameters, which is crucial when the computational models of liquid water are used for simulations in different environments, such as proteins, or for interaction with solutes.