  The simplest prescription for building a patterned structure from its
constituents is to add particles, one at a time, to an appropriate template.
However, self-organizing molecular and colloidal systems in nature can evolve
in much more hierarchical ways. Specifically, constituents (or clusters of
constituents) may aggregate to form clusters (or clusters of clusters) that
serve as building blocks for later stages of assembly. Here we evaluate the
character and consequences of such collective motion in a set of prototypical
assembly processes. We do so using computer simulations in which a system's
capacity for hierarchical dynamics can be controlled systematically. By
explicitly allowing or suppressing collective motion, we quantify its effects.
We find that coarsening within a two dimensional attractive lattice gas (and an
analogous off-lattice model in three dimensions) is naturally dominated by
collective motion over a broad range of temperatures and densities. Under such
circumstances, cluster mobility inhibits the development of uniform coexisting
phases, especially when macroscopic segregation is strongly favored by
thermodynamics. By contrast, the assembly of model viral capsids is not
frustrated but is instead facilitated by collective moves, which promote the
orderly binding of intermediates consisting of several monomers.
