Nucleation processes of naci and csf crystals from aqueous solutions studied by molecular dynamics simulations

Abstract

Nucleation processes of NaCI and CsF crystals from supersaturated aqueous solutions of (a) 9.25, and (b) 15.42 mol (kg H20)“1 NaCI and (c) 36.34 mol (kg H20)-l csf have been studied by molecular dynamics simulations. The periodically bound condition with the Ewald summation has been employed in the course of the simulation calculations. Numbers of cations (M+), anions (X-) and water (W) molecules in the systems (M+: X”; W) are (a) 56:56:336, (b) 80:80:288, and (c) 127:127:194. All ions and water molecules have been first randomly distributed in the cells and, except for (a), water molecules have been allowed to move until the thermal equilibrium attains between the water molecules and the ions which have been fixed at the given lattice points. Then, the simulation for the nucleation has been started. In (a) all water molecules and ions have been allowed to move freely in the pre-equilibrium step. Temperature has been kept constant at 298 K. Potential functions used in the simulations are the Fumi-Tosi, Kistenmacher-Popkie-Clementi, and Matsuoka-Clementi-Yoshimine potentials for ion-ion, ion-water, and water-water interactions, respectively. The simulation procedure has been continued for 18 ps with the time step At = 1.0 fs. Formation of ion clusters in the systems was slow down after about 12 ps. © 1991 IUPAC