  We conduct molecular dynamics computer simulations of a system of
Lennard-Jones particles, polydisperse in both size and mass, at a fixed density
and temperature. We test for and quantify systematic changes in dynamical
properties that result from polydispersity, by measuring the pair distribution
function, diffusion coefficient, velocity autocorrelation function, and
non-Gaussian parameter, as a function of the degree of polydispersity. Our
results elucidate the interpretation of experimental studies of collective
particle motion in colloids, and we discuss the implications of polydispersity
for observations of dynamical heterogeneity, in both simulations of simple
liquids and colloid experiments.
