Fe and Mn atoms interacting with carbon nanotubes

We study the structural, electronic and magnetic properties of Fe and Mn monomers and dimers adsorbed on a semiconductor (8,0) single-wall carbon nanotube. Using spin-polarized total-energy ab initio calculations based on the density-functional theory, we find for both Fe and Mn monomers the hexagonal center as the most stable adsorption site. For Fe dimers in the most stable configuration, the atoms are on opposite C-C bond-centered positions (BC-BC), with an Fe-Fe distance of 2.23 Angstrom. For Mn dimers, on the other hand, the most stable configurations are found to be with the Mn atoms adsorbed on top of C atoms, for a high-spin state (Mn-Mn distance of 2.6 Angstrom), and a slightly lower-energy BC-BC configuration for the low-spin state (Mn-Mn distance of 2.53 Angstrom). These results show that the dimer configurations are not simply related to the isolated monomer structures. The resulting magnetic moments for the adsorbed dimers are found to be similar to their corresponding values in the free diatomic molecules. (C) 2003 Elsevier B.V. All rights reserved.