Interaction of Impurity Atom with C60 Fullerene Cage: A Density Functional Theory (DFT) Analysis

We report the ground state geometry and electronic structure of MC60 clusters (M=Rb, Sr, Hf, Ga, Ge, Zn, As, Br). The calculations are performed using the density functional theory formalism under the Perdew-Burke-Erzerhof (PBE) exchange correlation energy functional. It is found that the preferred location of the M atom depends on their atomic size and nature of interaction with C-60 cage. While metal atoms like Sr, and Hf prefer encapsulation inside the cage by coordinating the hexagonal face, Ga caps the pentagon from outside. Among other atoms, Ge and As adsorb on the bridge site of the cage and Br sits on the top site. The stability analysis based on total energy considerations suggest that while Hf doping enhances the stability most, Zn with C-60 shows weakest interaction. In order to understand the energy barrier to insert impurity atom inside the cage wall, detailed calculations have been carried out to draw the energy landscape along the target path of 8.3 angstrom distance as the impurity atoms travel from outside (5 angstrom) to the center of the cage.