Sodium Chloride in Supercritical Water as a Function of Density: Potentials of Mean Force and an Equation for the Dissociation Constant from 723 to 1073 K and from 0 to 0.9 g/cm3

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• 作者：Wenbin Liu ; Robert H. Wood ; Douglas J. Doren
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：June 19, 2008
• 年：2008
• 卷：112
• 期：24
• 页码：7289 - 7297
• 全文大小：355K
• 年卷期：v.112,no.24(June 19, 2008)
• ISSN：1520-5207

文摘

The potential of mean force (PMF) of sodium chloride in water has been calculated by using the ab initio classical free-energy perturbation method at five state points: at 973 K with densities of 0.2796, 0.0935, and 0.0101 g/cm³ and at 723 K with densities of 0.0897 and 0.0098 g/cm³. The method is based on a QM-MM model in which Na−H₂O, Cl−H₂O, and Na−Cl interactions are calculated by ab initio methods. The water−water interactions are from the polarizable TIP4P-FQ model. The logarithm of the dissociation constant (log K_c) has been calculated from the PMF. These predictions, together with experimental measurements, were used to derive an equation for log K_c at densities from 0 to 0.9 g/cm³ and temperatures from 723 to 1073 K, as well as from 600 to 1073 K for densities from 0.29 g/cm³ to 0.9 g/cm³. Extrapolation of the present equation below 723 K for densities less than 0.29 g/cm³ does not fit the experimental results. This is attributed to long-range changes in the local dielectric constant due to the high compressibility. Comparisons with previous predictions and simulations are presented.