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

Abstract

A systematic study of Mn monomers, dimers, trimers, and wires interacting with an (8, 0)semiconductor single-wall carbon nanotube (SWCN) is presented. Spin-polarizedtotal-energy ab initio calculations based on the density functional theory are used todescribe the structural, electronic and magnetic properties of all studied systems. For Mnmonomers, either outside or inside the nanotube, the most stable configuration is found tobe over the centre of the hexagonal site. The most stable geometry for outsidedimers presents the Mn atoms adsorbed directly on top of C atoms, when in ahigh-spin configuration, whereas for a low-spin configuration the Mn atoms areadsorbed on bond-centred sites at opposite sides of a hexagonal ring, with theMn–Mn bond aligned in a diagonal direction relative to the tube axis in bothcases. There are many low energy configurations (at above the lowest energy ones) at distinct orientations, for both the low and high energyconfigurations. 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 approximately1 eV/Mn atom. A monoatomic wire in a zig-zag configuration has a binding energy that isintermediate between the open and the compact trimers, independently of the spinconfiguration. For all the investigated Mn structures adsorbed on the SWCN, eitherhigh-spin (HS) or low-spin (LS), the interactions between Mn atoms and between Mn andC atoms become stronger as the Mn coordination number increases. The resulting magneticmoments for all adsorbed systems are found to be close to their original values for thecorresponding free Mn structures.