Effects of different hydrogen distributions on the magnetic properties of hydrogenated single-walled carbon nanotubes

The magnetic properties of the hydrogenated single-walled carbon nanotubes (SWNTs) have been studied by the first-principles calculations. It is found that different distributions of hydrogen atoms on the SWNT surfaces have a significant effect on the magnetic order of the hydrogenate SWNTs. More importantly, it has been shown that in general there exist two types of the hydrogen adsorption sites on the SWNT external surface, forming two different structures of the hydrogenated SWNTs, i.e., the so-called AA and AB structure, among which the latter has lower total energy than the former. The flat bands appear at the Fermi energy in the AA structures, favoring spontaneous magnetism, but not in the AB structures, making the composite system always stay in the nonmagnetic ground state.