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Ab initio study of the influence of adsorbed atoms on vacancy-induced magnetic moments in graphene sheets

We present ab initio calculations for single-atom vacancies in graphene. In agreement with earlier work, we find that vacancies are responsible for the magnetism recently observed experimentally, creating a center with net spin. For small supercells, there is a strong symmetry breaking in the supercell with respect to the perfect graphene structure, and this symmetry breaking is much smaller for larger supercells. The influence of the adsorption of H, O and N atoms on the spin center of the bare single-atom vacancy and its influence on the magnetism induced in these samples is investigated. A rich variety of mechanisms is found for the generation of magnetism in this system.