ION SOLVATION IN SUPERCRITICAL WATER-BASED ON AN ADSORPTION ANALOGY

The solvation structure and free energy for Li+, Na+, K+, F-, Cl-, Be2 +, Mg2+, and Ca2+ in supercritical aqueous solutions are described by a dielectric concentric shell model incorporating solvent adsorption a nalogous to a Langmuir model, The ratio of solvent bulk density to the local density in the first coordination shell of alkali and halide io ns obtained from molecular dynamics simulation is shown to be linear i n bulk density at supercritical temperatures, justifying the model, Th e model utilizes two parameters: a maximum local density, which is fou nd to be insensitive to temperature and correlated with the surface fi eld, and a desorption constant, which we find may be approximated as z ero in the free energy calculations. In comparison to the Born model, free energies of solvation predicted by the concentric shell model sho w far better agreement with values from full molecular simulation and with those from a compressible continuum model.