Hydrodynamic behaviour of a solute particle by molecular dynamics

Abstract

The hydrodynamic behaviour of a single solute particle immersed in a solvent system of (N-1 particles, interacting through a repulsive Lennard-Jones potential, has been studied for several system sizes, ranging from N = 108 to 2048 particles using isothermal-isochoric molecular dynamics computer simulation. The solute particle was projected at a fixed relative velocity with respect to the host fluid. The computations show that the linear resistance force versus velocity behaviour, postulated by the Stokes law, is obeyed quite well even up to relatively large (i.e. near thermal) solute velocities. However, two finite size effects have been found for large solute particles (cα σB/σs > 1, where σBand σs the solute and solvent particles, respectively) when they are confined in such small periodic systems. At high drift velocity, there is a breakdown in this linear relationship for the smaller systems leading to a maximum in the opposing force on the solute particle. Als o there is a slow system size convergence to the thermodynamic (N → ∞ effective Stokes c parameter, and when compared with the value given by the Stokes-Einstein relationship.