Anomalous change in the dynamics of a supercritical fluid.

We perform molecular dynamics simulations to investigate dynamical properties of a supercritical Lennard-Jones fluid. We find that in the supercritical region there is a short-ranged deviation in dynamic character. We further find that this anomalous change is associated with the presence of the Widom line, the locus of specific heat maxima, of the liquid-vapor phase transition. The salient change in dynamics is consistent with a crossover in the correlation of the diffusion coefficient with the excess entropy. Our results lead to an interpretation that, even though a supercritical fluid excludes a singularity, its dynamical properties can be significantly affected by the existence of thermodynamic response maxima.