Molecular Dynamics Simulation of Aqueous MNO3 (M = Li, Na, K, Rb, and Cs) Solutions

Abstract

Abstract To understand the anisotropy, cation dependence, and concentration dependence of the orientational relaxation time of the nitrate ion, the structure and molecular motion were studied by molecular dynamics simulation of MNO3 (M = Li, Na, K, Rb, and Cs) solutions. The interaction parameters determined for the molten salt were used between the ions. The Carravetta–Clementi potential was assumed for the water–water pair. An empirical combination rule was adopted in the water-ion interactions. Simulations were done at several volumes corresponding to the normal density and low pressures. The temperature was 300 K and the concentrations was 1 or 2 mol kg−1. The distribution of water molecule is almost isotropic around the nitrate ion. No water molecules are found which move in strong correlation with the rotation of the nitrate ion. The calculated orientational relaxation time of the nitrate ion is in agreement with the experimental results qualitatively with respect to its anisotropy, cation dependence, and concentration dependence. These were analyzed by the potential energy of the species around the nitrate ion. The anisotropy of the relaxation time was due to the anisotropic charge distribution in the nitrate ion, as demonstrated by several models.