Self-diffusion of large solid clusters in a liquid by molecular dynamics simulation

Abstract

Molecular dynamics simulations have been carried out of rigid and dynamic solid near-spherical atomistically discrete Lennard-Jones (LJ) clusters in a WCA host liquid. A single cluster consisted of 5–256 LJ particles in systems containing up to 27000 particles in total. The diffusion coefficients were found to be insensitive to the nature of the degrees of freedom of the cluster. Rigid clusters, with no internal degrees of freedom, gave essentially the same self-diffusion coefficients as those composed of thermally interacting LJ atoms. The diffusion coefficients decrease with cluster size and increase with system size. For clusters in excess of 100 particles, system sizes of at least 10000 particles are required to attain the thermodynamic limit. In the thermodynamic limit, the Stokes-Einstein relationship is obeyed approximately, assuming an increase in the local viscosity of the liquid around the cluster, as a consequence of an observed enhanced local order in this region. We have shown that clusters of several hundred atoms exhibit classical Langevin dynamics, with near exponential long-term decay of the force and velocity autocorrelation functions. The large clusters exhibit slow reorientational relaxation compared with that of angular frequency.