  In materials science, wedge disclinations are defects caused by angular
mismatches in the crystallographic lattice. To describe such disclinations, we
introduce an atomistic model in planar domains. This model is given by a
nearest-neighbor-type energy for the atomic bonds with an additional term to
penalize change in volume. We enforce the appearance of disclinations by means
of a special boundary condition.
  Our main result is the discrete-to-continuum limit of this energy as the
lattice size tends to zero. Our proof method is relaxation of the energy. The
main mathematical novelty of our proof is a density theorem for the special
boundary condition. In addition to our limit theorem, we construct examples of
planar disclinations as solutions to numerical minimization of the model and
show that classical results for wedge disclinations are recovered by our
analysis.
