  Hard-sphere model systems are well-suited in both experiment and simulations
to investigate fundamental aspects of the crystallization of fluids. In
experiments on colloidal models of hard-sphere fluids, the uid is unavoidably
at contact with the walls of the sample cell, where heterogeneous
crystallization may take place. In this work we use simulations to investigate
the competition between homogeneous and heterogeneous crystallization. We
report simulations of wall-induced nucleation for different confining walls.
Combining the results of these simulations with earlier studies of homogeneous
allows us to asses the competition between homogeneous and heterogeneous
nucleation as a function of wall type, fluid density and the system size. On at
walls, heterogeneous nucleation will typically overwhelm homogeneous
nucleation. However, even for surfaces randomly coated with spheres with a
diameter that was some three times larger than that of the fluid spheres - as
has been used in some experiments - heterogeneous nucleation is likely to be
dominant for volume fractions smaller than 0.535. Only for a disordered coating
that has the same structure as the liquid holds promise did we find the
nucleation was likely to occur in the bulk. Hence, such coatings might be used
to suppress heterogeneous nucleation in experiments. Finally, we report the
apparent homogeneous nucleation rate taking into account the formation of
crystallites both in the bulk and at the walls. We find that the apparent
overall nucleation rates coincides with those reported in "homogeneous
nucleation" experiments. This suggests that heterogeneous nucleation at the
walls could partly explain the large discrepancies found between experimental
measurements and simulation estimates of the homogeneous nucleation rate.
