  Using overdamped Brownian dynamics simulations we investigate the
isotropic-nematic (IN) transition of self-propelled rods in three spatial
dimensions. For two well-known model systems (Gay-Berne potential and hard
spherocylinders) we find that turning on activity moves to higher densities the
phase boundary separating an isotropic phase from a (nonpolar) nematic phase.
This active IN phase boundary is distinct from the boundary between isotropic
and polar-cluster states previously reported in two-dimensional simulation
studies and, unlike the latter, is not sensitive to the system size. We thus
identify a generic feature of anisotropic active particles in three dimensions.
