  Charged colloidal particles - both on the nano and micron scales - have been
instrumental in enhancing our understanding of both atomic and colloidal
crystals. These systems can be straightforwardly realized in the lab, and tuned
to self-assemble into body-centered cubic (BCC) and face-centered cubic (FCC)
crystals. While these crystals will always exhibit a finite number of point
defects, including vacancies and interstitials - which can dramatically impact
their material properties - their existence is usually ignored in scientific
studies. Here, we use computer simulations and free-energy calculations to
characterize vacancies and interstitials in both FCC and BCC crystals of
point-Yukawa particles. We show that, in the BCC phase, defects are
surprisingly more common than in the FCC phase, and the interstitials manifest
as so-called crowdions: an exotic one-dimensional defect proposed to exist in
atomic BCC crystals. Our results open the door to directly observing these
elusive defects in the lab.
