  We report a computer-simulation study of the equilibrium phase diagram of a
three-dimensional system of particles with a repulsive step potential. The
phase diagram is obtained using free-energy calculations. At low temperatures,
we observe a number of distinct crystal phases. We show that at certain values
of the potential parameters the system exhibits the water-like thermodynamic
anomalies: density anomaly and diffusion anomaly. The anomalies disappear with
increasing the repulsive step width: their locations move to the region inside
the crystalline phase.
