(730a) A Gaussian-Charge Polarizable Model for Water

Force fields for water that explicitly account for polarization effects are expected to provide reasonable estimates of water properties for wide range of conditions. Such models are, among others, the BK3 [1], GCPM [2] and SWM4-NDP [3] models. These polarizable force fields generally show better performance compared to non-polarizable ones in description of properties for pure water and aqueous electrolyte solutions. [4] However, for the water and carbon dioxide mixture, which is of great significance to the design of carbon dioxide geologic sequestration, the calculation of its equilibrium phase compositions using existing polarizable water models are far from satisfactory, even when the carbon dioxide/water cross interaction was optimized. In this study, a polarizable force field was developed for water with the aim of improving the prediction of thermophysical properties for carbon dioxide/water mixture. The proposed water force field has a rigid geometry with bond angle and length setting to their experimental values. The van der Waals interaction is represented by the Buckingham Exponential-6 potential assigned on the oxygen atom. The electrostatic interactions are represented by Gaussian charge instead of point charge for its greater numerical stability. The polarization of water molecule is handled via classical Drude oscillator by attaching a single negative Gaussian charge to the oxygen atom with a harmonic spring, and the spring constant is set to reproduce the experimental molecular polarizability of water. An explicit and analytical hydrogen bond term is used in the model to account for possible charge transfer effects happening in water hydrogen bonds. The model was parameterized to the properties of water at ambient conditions, including configuration energy, density, partial pair correlation functions, dielectric constant, as well as the minimum energy and geometry of water dimer. The proposed model was tested against a variety of properties including temperature of maximum density, heat capacity, compressibility, second virial coefficient, saturated vapor-liquid phase densities, vapor pressure, enthalpy of vaporization, vapor-liquid interfacial tension, melting point, viscosity and diffusion coefficient. With the proposed polarizable water model, the phase equilibrium properties of the carbon dioxide/water mixture were studied.

[1] Kiss, P.; Baranyai, A. J. Chem. Phys. 2013, 138, 204507.

[2] Paricaud, P.; Predota, M.; Chialvo, A. A.; Cummings, P. T. J. Chem. Phys. 2005, 122, 244511.

[3] Lamoureux, G.; Harder, E.; Vorobyov, I. V.; Roux, B.; MacKerell, A. D. Chem. Phys. Lett. 2006, 418, 245.

[4] Jiang, H.; Mester, Z.; Moultos, O. A.; Economou, I. G.; Panagiotopoulos, A. Z. J. Chem. Theory. Comput. 2015, 11, 3802.