  We simulate a model of self-propelled disks with soft repulsive interactions
confined to a box in two dimensions. For small rotational diffusion rates,
monodisperse disks spontaneously accumulate at the walls. At low densities,
interaction forces between particles are strongly inhomogeneous, and a simple
model predicts how these inhomogeneities alter the equation of state. At higher
densities, collective effects become important. We observe signatures of a
jamming transition at a packing fraction $\phi \sim 0.88$, which is also the
jamming point for non-active athermal monodisperse disks. At this $\phi$, the
system develops a critical finite active speed necessary for wall aggregation.
At packing fractions above $\phi \sim 0.6$, the pressure decreases with
increasing density, suggesting that strong interactions between particles are
affecting the equation of state well below the jamming transition. A mixture of
bidisperse disks segregates in the absence of any adhesion, identifying a new
mechanism that could contribute to cell sorting in embryonic development.
