Application of the uniform source-and-sink scheme to molecular dynamics calculation of the self-diffusion coefficient of fluids

A uniform source-and-sink scheme was developed by Cao and Li [J. Chem. Phys. 133 (2010), 024106] to calculate the thermal conductivity of solid argon. Now, we aim to apply this scheme to the calculation of the self-diffusion coefficient. We divide the particles into equal halves, and label them with A or B. By exchanging the labels of individual atoms from the right and left half systems, we can produce an internal matter flux, and hence the internal matter source and sink can be realized. The density profile is piecewise quadratic throughout the system and the self-diffusion coefficient can be easily extracted from the mean densities of the right and left half systems rather than by fitting the density profile. In particular, this is a nonequilibrium molecular dynamics method but established on an equilibrium system. The scheme is applied to calculate the self-diffusion coefficient by taking a Lennard-Jones fluid as a case, examining its homogeneity, convergence, label exchange interval, and dependence on density, temperature, and system size. The uniform source-and-sink scheme is demonstrated to be able to give accurate results with fast convergence.