  This study uses a combination of stochastic optimization, statistical
mechanical theory, and molecular simulation to test the extent to which the
long-time dynamics of a single tracer particle can be enhanced by rationally
modifying its interactions--and hence static correlations--with the other
particles of a dense fluid. Specifically, a simulated annealing strategy is
introduced that, when coupled with test-particle calculations from an accurate
density functional theory, finds interactions that maximize either the tracer's
partial molar excess entropy or a related pair-correlation measure (i.e., two
quantities known to correlate with tracer diffusivity in other contexts). The
optimized interactions have soft, Yukawa-like repulsions, which extend beyond
the hard-sphere interaction and disrupt the coordination-shell cage structure
surrounding the tracer. Molecular and Brownian dynamics simulations find that
tracers with these additional soft repulsions can diffuse more than three times
faster than bare hard spheres in a moderately supercooled fluid, despite the
fact that the former appear considerably larger than the latter by conventional
definitions of particle size.
