  Cobalt-related impurity centers in diamond have been studied using first
principles calculations. We computed the symmetry, formation and transition
energies, and hyperfine parameters of cobalt impurities in isolated
configurations and in complexes involving vacancies and nitrogen atoms. We
found that the Co impurity in a divacant site is energetically favorable and
segregates nitrogen atoms in its neighborhood. Our results were discussed in
the context of the recently observed Co-related electrically active centers in
synthetic diamond.
