  It has recently been shown that identical, isotropic particles can form
complex crystals and quasicrystals. In order to understand the relation between
the particle interaction and the structure, which it stabilizes, the phase
behavior of a class of two-scale potentials is studied. In two dimensions, the
phase diagram features many phases previously observed in experiment and
simulation. The three-dimensional system includes the sigma phase with 30
particles per unit cell, not grown in simulations before, and an amorphous
state, which we found impossible to crystallize in molecular dynamics. We
suggest that the appearance of structural complexity in monodisperse systems is
related to competing nearest neighbor distances and discuss implications of our
result for the self-assembly of macromolecules.
