Fluid transport properties by equilibrium molecular dynamics. II. Multicomponent systems

The Green-Kubo formalism for evaluating transport coefficients by molecular dynamics has been applied to multicomponent mixtures of flexible, multicen ter models of linear and branched alkanes and nitrogen and helium in the ga s phase and in the liquid phase. Simulation results on binary systems are s ummarized and trends in prediction using simple but realistic molecular mod els are shown. New simulation results of N-2-n-pentane agree with experimen t with a maximum deviation of 36%, the greatest error being for pure n-pent ane. Methodological aspects of simulating multicomponent systems with trace components are studied, varying the system size and molecular interaction potentials. It is shown that mixtures are treated representatively even whe n only one to two molecules of a species are present in the simulated syste m, unless there is an extreme degree of self-association. It is demonstrate d that molecular dynamics may predict quantitatively (7% and 11% deviation) the viscosity of a seven component "synthetic" natural gas. (C) 1999 Ameri can Institute of Physics. [S0021-9606(99)51008-8].