DYNAMIC PROPERTIES OF COULOMBIC SYSTEMS AT LOW-DENSITIES - COMPUTER-SIMULATION RESULTS

Both nonequilibrium and equilibrium molecular dynamics techniques have been employed in order to obtain mechanical transport coefficients for Coulombic systems at low densities. These computer experiments, in which the response of the systems to applied electrical fields varying in magnitude and frequency was investigated, were carried out under isothermal conditions. In the static field nonequilibrium molecular dynamics (NEMD) simulations the influence of the field strength on the static conductivities has been examined in detail; linear field dependence was obtained over a wide range of applied fields for all studied densities. Nonspherical distributions of ions, as well as spatial oscillations of the ionic density, were observed in the systems subjected to strong electrical fields. The frequency-dependent electrical conductivities were evaluated in nonequilibrium simulations with alternating fields and were found to be in a good quantitative agreement with the spectra obtained from equilibrium calculations. Generally, the NEMD technique proved to be particularly efficient for these ionic systems in the low density regime. Comparison was also made with the data available from kinetic (Chapman-Enskog) theory and it was found that the concentration dependence of the self-diffusion coefficients demonstrates a systematic deviation from the simulation results.