Monte Carlo simulation of supercritical solutions in the grand canonical ensemble

Molecular simulations have been undertaken of pure, repulsive, and attractive supercritical Lennard-Jones solutions using the Monte Carlo technique in the grand canonical ensemble for the same systems and states used in a previous study by the molecular dynamics technique in the canonical ensemble. The pure supercritical fluid exhibited structure which differed somewhat between the canonical and grand canonical simulations at distances of three or four diameters from a central particle. The grand canonical simulation was shown to have chemical potential in agreement with the calculations from the equation of state and to be thermodynamically consistent. Simulations of the repulsive mixture in the grand canonical ensemble were characterized by substantial statistical scatter so that the special capabilities of the grand canonical simulation -- fluctuation analysis and thermodynamic consistency testing -- could not be employed. The attractive supercritical mixture studied previously was found to be within the two-phase region when studied in the grand canonical ensemble. The only previous simulation of mixtures in the grand canonical ensemble did not attempt to apply the fluctuation analysis or the thermodynamic consistency test; so, the negative results of this work are new.