  Diffusion of self-propelled particles in the presence of randomly distributed
obstacles in three dimensions is studied using molecular dynamics simulations.
It is found that depending on the magnitude of the propelling force and the
particle aspect ratio, the diffusion coefficient can be a monotonically
decreasing or a non-monotonic concave function of the obstructed volume
fraction. Counterintuitive enhancement of the particle diffusivity with
increasing the obstacles crowd is shown to be a combinatory effect of the
self-propelling force and the anisotropy in the shape of the particle. Regions
corresponding to monotonic and non-monotonic dependence of the particle
diffusivity on the obstacle density in propelling force-aspect ratio plane are
specified theoretically and using the simulation results.
