First-Principles Calculations of Hydrogen Monomers and Dimers Adsorbed in Graphene and Carbon Nanotubes

By using first-principles electronic structure calculations, we study hydrogen monomers and dimers in graphene, the armchair edge (5; 5) carbon nanotube (CNT), and the zigzag edge (10; 0) CNT. We find that the monomers in the above three carbon nanomaterials have a magnetic moment of 1 mu(B). In the case of the CNTs, the hydrogen atoms are located on the outer side of the CNTs. In the most stable structures of the dimers in the above three carbon materials, the two hydrogen atoms are bonded to host carbon atoms which are nearest-neighbors. In the case of graphene, the two atoms are located on opposite sides, whereas in the case of the armchair edge (5, 5) CNT and zigzag edge (10, 0) CNT, both hydrogen atoms are located on the outer side. The electronic structures of the most stable geometries are found to be nonmagnetic. However, when the two hydrogen atoms are bonded to second-nearest-neighbor carbon atoms, the magnetic moment is found to be 2 mu(B).