An ab initio study of manganese atoms and wires interacting with carbon nanotubes

A systematic study of Mn monomers, dimers, trimers, and wires interacting with an (8, 0) semiconductor single-wall carbon nanotube (SWCN) is presented. Spin-polarized total-energy ab initio calculations based on the density functional theory are used to describe the structural, electronic and magnetic properties of all studied systems. For Mn monomers, either outside or inside the nanotube, the most stable configuration is found to be over the centre of the hexagonal site. The most stable geometry for outside dimers presents the Mn atoms adsorbed directly on top of C atoms, when in a high-spin configuration, whereas for a low-spin configuration the Mn atoms are adsorbed on bond-centred sites at opposite sides of a hexagonal ring, with the Mn-Mn bond aligned in a diagonal direction relative to the tube axis in both cases. There are many low energy configurations (at similar or equal to0.1 eV above the lowest energy ones) at distinct orientations, for both the low and high energy configurations. For trimers, two kinds of Mn structures are investigated: compact or open. The compact trimers are found to be more stable than the open systems by approximately 1 eV/Mn atom. A monoatomic wire in a zig-zag configuration has a binding energy that is intermediate between the open and the compact trimers, independently of the spin configuration. For all the investigated Mn structures adsorbed on the SWCN, either high-spin (HS) or low-spin (LS), the interactions between Mn atoms and between Mn and C atoms become stronger as the Mn coordination number increases. The resulting magnetic moments for all adsorbed systems are found to be close to their original values for the corresponding free Mn structures.