BOUNDARY-CONDITIONS IN SIMULATIONS OF AQUEOUS IONIC-SOLUTIONS - A SYSTEMATIC STUDY

The room temperature properties of aqueous solutions of SPC, TIP4P, an d MCY water are examined using either a potential cutoff or Ewald summ ation. The effects of interaction truncation are compared to the impor tance of the medium (vacuum or metal) that the entire system is immers ed in; for this purpose simulations an also carried out in which the u nit cell surface polarization term of De Leeuw, Perram, and Smith (Pro c. R. Soc. London 1980, A373, 27) is explicitly accounted for. Both pu re water and dilute solutions of Cl- and Fe2+ are investigated. It is found that not only solvent-solvent orientational correlations but als o ion-solvent energies, ion-induced solvent reorganization energies, a nd ionic diffusion coefficients can be exceedingly sensitive to the na ture of the surroundings. It is asserted that reaction field methods a nd Ewald summation are the preferred types of boundary conditions, but that the method of parametrization of the potential functions has to be consistent with the eventual simulation conditions.