(534d) Polarization and the Thermophysical Properties of Water and Aqueous Mixtures

Water plays a near ubiquitous role in biological, chemical and industrial processes. Historically, predicting the properties of water involved either empirical correlations or equation of state modelling [1], [2], whereas more recently molecular simulation [3] has become he method of choice because of the nexus between underlying intermolecular interactions and observable macroscopic properties. The availability of an intermolecular potential to evaluate inter-particle forces or energies is the key to accurate predictions. There are many alternative intermolecular potentials for water [4], although the basis of many water potentials is at best semi-empirical. The most widely used models are rigid and variants of either the four-site transferable interaction potential (TIP4P) or the three-site simple point charge (SPC, SPC/E) models. The appeal of such potentials is computational expedience and in many cases they have provided worthwhile predictions. However, comparisons with experiment are often focused at relatively low temperatures and pressures, with a temperature of 25 ºC and a pressure of 1 atmosphere being a popular choice.

The explicit incorporation of the effects of polarization is an aspect that has been largely missing from many simple water potentials. Recent work [5], using an ab initio based potential strongly indicates that including polarization greatly improves the accuracy of predictions. In this work, we report phase equlibria, thermodynamic properties and diffusion simulation data for both water and aqueous mixtures obtained by accounting for polarization effects. A comparison is also given with both experimental data and calculations using traditional potentials such as TIP4P/2005, SPC and SPC/E potentials over a wide range of temperatures and pressures. In many cases including polarization results in almost perfect agreement with experiment and as such is more accurate than can be obtained from conventional approaches. Significantly, the improvement gained in accuracy was achieved without resorting to fitting theory to experiment and as such the calculations represent genuine a priori predictions. The ability to make accurate predictions is particularly important for the study of aqueous mixtures for which experimental data is often more limited than that for pure water. 

[1] Y. Wei and R. J. Sadus, AIChE J. 2000, 46, 169-196 ; N. G. Stetenskaja, R. J. Sadus and E. U. Franck, J. Phys. Chem. 1995, 99, 4273 -4277 ; A. E. Mather, R. J. Sadus and E. U. Franck, J. Chem. Thermodyn. 1993, 25, 771-779.

[2] W. Wagner and A. Pruß, J. Phys. Chem. Ref. Data. 2002, 31, 387-535.

[3] R. J. Sadus, Molecular Simulation of Fluids: Theory, Algorithms and Object-Orientation, Elsevier, Amsterdam, 1999.

[4] C. Vega and J. L. F. Abascal, Phys. Chem. Chem. Phys. 2011, 13, 19663.

[5] T. M. Yigzawe and R. J. Sadus, J. Chem. Phys. 2013, 138, 044503; I. Shvab and R. J. Sadus, Phys. Rev. E, 2012, 85, 051509; I. Shvab and R. J. Sadus, J. Chem. Phys. 2012, 137, 124501.