Nanostructures of C₆₀-metal-graphene (metal = Ti, Cr, Mn, Fe, or Ni): A spin-polarized density functional theory study

We used plane-wave density functional theory (DFT) to investigate the properties of C₆₀-M-graphene (C₆₀-M-G) nanostructures (M = Ti, Cr, Mn, Fe, or Ni). The calculated binding energies suggested that C₆₀ could be mounted on a metal-graphene surface with good bonding stability. The high-spin C₆₀-Cr-G nanostructure was found to be more stable than the previously reported low-spin configuration. Also, C₆₀-Ti was found to stand symmetrically upright on the graphene surface, while in the remaining four cases, the orientation of C₆₀-M in the C₆₀-M-G nanostructures were bent, and the geometry of each structure is somewhat different, depending on the identity of the bridging metal atom. The large geometric distortion of C₆₀-M in the tilted C₆₀-M-G nanostructures (with Cr, Fe, Mn, and Ni) is attributed to the spin polarization in the 3d orbitals and dispersion interactions between graphene and C₆₀. Additional DFT calculations on smaller C₆₀-M-benzene complexes with atomic-orbital (AO) basis sets provided consistent results on structural geometry and numbers of unpaired electrons. The DFT calculations using AO basis sets suggested that the C₆₀-M unit was flexible with respect to the bending motion. The knowledge of metal-dependent geometric differences derived in this study may be useful in designing nanostructures for spintronic and electronic applications.