Computer simulation of sedimentation of ionic systems using the Wolf method.

We present computer simulation results for 1:1 and 2:1 electrolyte solutions in the presence of a gravitational field, using the Monte Carlo method in the NVT ensemble for the restrictive primitive model. Coulombic interactions were taken into account comparing the Ewald and Wolf methods. Three variations of Ewald summations were considered: the exact method for slab geometries (EW2D), and the three-dimensional (3D) versions with and without a dipolar correction (EW3DC and EW3D, respectively). The equivalent 3D Wolf protocols were applied under the same conditions (WF3DC and WF3D, respectively). The Wolf and Ewald methods agree accurately in the prediction of several thermodynamic and structural properties for these inhomogeneous systems: excess internal energies, isochoric heath capacities, and density and electrostatic potential profiles. The main advantage using the Wolf method is the significant saving in computing time, which is approximately six times faster than EW3D and EW3DC, and sixty times faster than EW2D.