The Structural, Energetic and Electronic Properties of Doped Carbon   Nanotubes by Encapsulation of MCp2 (M=Fe, Co, Ni): a Theoretical   Investigation
  Metallocenes can be encapsulated inside the carbon nanotubes. The structural, energetic and electronic properties of organometallic MCp2@SWCNT are obtained from DFT method. We verify that such encapsulation is noncovalent functionalization, and examined binding energies and charge transfers of MCp2@(16,0)SWCNT systems. Consistent with recent experimental findings, the optimal distance between FeCp2 center and near tube-wall is 4.7 (5.1) {\AA} for the configuration where MCp2's five-fold axis is parallel (vertical) to nanotube axis, while the minimal diameter is 9.4 (10.2) {\AA} to exothermically encapsulate FeCp2 molecules. Finally we clarify the doping effects near the bandgap by encapsulations of CoCp2 and NiCp2. 
Fenglei Cao, Wei Ren, Xianfang Xu, Ye-Xiang Tong, and Cunyuan Zhao
cond-mat.mtrl-sci