Molecular Dynamics Simulations of Freezing Behavior of Pure Water and 14% Water-NaCl Mixture Using the Coarse-Grained Model

Abstract

We performed molecular dynamics simulations using the coarse-grained model to study the freezing behavior of pure water and 14% water-salt mixture in a wide range of temperatures for a very long time around 50 nanoseconds. For the salty water, an interface in nanoscale was used. For both systems, the freezing behavior of water molecules was studied using some qualities such as density, total energy, and radial distribution function. For the 14% water-salt mixture, the equilibrium freezing temperature depression observed in the simulations was well consistent with the experimental data. Contrary to the water-salt mixture, however, the above- mentioned quantities changed dramatically for the pure water at the freezing point. The plots of the total energy versus time shows the freezing point of 14% water-salt mixture was 265 K that is 9 K less than the freezing point of pure water. The reduction of freezing point is in very good agreement with the experimental freezing point. The results of the simulation showed that in the less temperature than obtained freezing point, the sodium and chloride ions tendency to network formation and rejection of solution lead to reduction of water molecules accumulation.