  Inverse design can be a useful strategy for discovering interactions that
drive particles to spontaneously self-assemble into a desired structure. Here,
we extend an inverse design methodology--relative entropy optimization--to
determine isotropic interactions that promote assembly of targeted
multicomponent phases, and we apply this extension to design interactions for a
variety of binary crystals ranging from compact triangular and square
architectures to highly open structures with dodecagonal and octadecagonal
motifs. We compare the resulting optimized (self and cross) interactions for
the binary assemblies to those obtained from optimization of analogous
single-component systems. This comparison reveals that self interactions act as
a `primer' to position particles at approximately correct coordination shell
distances, while cross interactions act as the `binder' that refines and locks
the system into the desired configuration. For simpler binary targets, it is
possible to successfully design self-assembling systems while restricting one
of these interaction types to be a hard-core-like. However, optimization of
both self and cross interaction types appears necessary to design for assembly
of more complex or open structures.
