The mutual diffusion constant of a binary mixture of equal diameter hard spheres was estimated using the method of molecular dynamics. The mixture considered was equimolar, with a species mass ratio often to one in a volume that was three times the close-packed volume. Two molecular dynamics methods were used: the standard Green-Kubo technique based on the evaluation of equilibrium velocity correlation functions, and a non-equilibrium method that generates a steady diffusive flow along a composition gradient by imposing special boundary conditions on two opposing faces of the cubic volume. It was found that both methods yield, within about 3%, the same value of the diffusion coefficient.

The Mutual Diffusion Constant of Binary, Isotopic Hard-Sphere Mixtures: Molecular Dynamics Calculations using the Green-Kubo and Steady-State Methods. Kincaid, J.M., Erpenbeck, J.J.:  The Journal of Chemical Physics, 1986, 84[6], 3418-31