Molecular Dynamics Study of Aqueous Solutions IX. Dynamical Properties of an NH₄Cl Solution

The dynamical properties of an aqueous ammonium chloride solution have been calculated from a molecular dynamics simulation over 3.5 picoseconds at a temperature of 301 K where the basic periodic cube contained 200 water molecules, 8 ammonium ions and 8 chloride ions. The effective pair potentials are based on the ST 2 water model, a rigid tetrahedral four point charge model for NH 4+ , and a single point charge model for CI - . The coefficients of self-diffusion and of rotational diffusion, the spectral densities of hindered translations and of librations, the correlation times of the dipole moment vector and the vector connecting the two protons in a water molecule are reported separately for the various subsystems - NH 4+ , Cl - , bulk water, hydration water of NH 4 + and CI - - and are compared with the available experimental data. Implications with respect to the structure breaking ability of the ions are discussed.