Nonequilibrium Molecular Dynamics Simulations of Molten Sodium Chloride

The main problems arising in all far-from-equilibrium simulations come from temperature control. When local flows become important, it is not a simple matter to distinguish between the flow velocity and thermal motion. A way to bypass this problem is to control the temperature given by the “configurational expression”, which does not depend on velocity. The responses of molten NaCl to strong shear and strong constant and oscillating electric fields using kinetic and configurational thermostats are compared. The differences in response increase with the increase in the external perturbation, and in very strong fields one can observe striking structural differences. In the case of shear flow, the differences are of a general nature seen in all liquids (the appearance of a string phase with kinetic thermostats), while in an electric field they are peculiar to ionic fluids and are related to the degree of dissociation. Some structural properties can be deduced by evaluating the configurational temperature expression.