title: 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/cm(3).
abstract: 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/cm (3) and at 723 K with densities of 0.0897 and 0.0098 g/cm (3). The method is based on a QM-MM model in which Na-H 2O, Cl-H 2O, 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/cm (3) and temperatures from 723 to 1073 K, as well as from 600 to 1073 K for densities from 0.29 g/cm (3) to 0.9 g/cm (3). Extrapolation of the present equation below 723 K for densities less than 0.29 g/cm (3) 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.
authors.affiliation: Quest Pharmaceutical Services, Newark, DE 19711, USA.
authors.forename: Wenbin
authors.initials: W
authors.lastname: Liu
authors.forename: Robert H
authors.initials: RH
authors.lastname: Wood
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Doren
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D006358:Hot Temperature; D007477:Ions / Q000737:chemistry*; D008956:Models, Chemical; D011789:Quantum Theory; D012965:Sodium Chloride / Q000737:chemistry*; D013046:Specific Gravity; D055672:Static Electricity; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D007477:Ions; D014867:Water; D012965:Sodium Chloride