First-principles study of structural stability, magnetism, and hyperfine coupling in hydrogen clusters adsorbed on graphene

Using first-principles electronic-structure calculations, we studied the structural and magnetic properties of various hydrogen clusters, including hydrogen monomer, dimers, trimers, tetramers, and hexamers adsorbed on a graphene surface. The magnetic behaviors of such defective systems were shown to strongly depend on the geometrical configuration of hydrogen atoms. The stability of the structures was demonstrated to be dependent on two important factors: the distance between hydrogen atoms and the strength of exchange couplings between the defect-induced magnetic moments. For the magnetic structures, the electron spins populate the quasilocalized p(z)-type states on specific carbon atoms. The presence of such quasilocalized p(z)-type states was shown to yield relatively strong hyperfine couplings at particular carbon sites in the neighborhood of hydrogen atoms.