Titanium-carbon Nanotubes And Endohedral Metallofullerenes: A DFT Investigation

Fullerene and carbon nanotubes have attracted much attention of the researchers due to their unique structure and rich electronic properties. The researches on nanocages and nanotubes are stimulated due to the great applications prospects of fullerene and carbon nanotubes in electronic devices, catalysts, magnetic materials and so on.In this paper, all the calculations are performed using density functional theory. Two kinds of novel single-walled titanium-carbon nanotubes are constructed based on Met-Car and their stabilities are predicted. The electronic structure of these nanotubes and the varbrition of it as the length of the nanotubes are calculated. Through a fictitious quasi-static process, the stabilities of the endohedral metallofullerenes are investigated in the paper. The quasi-static processes of Fe going into and out from C60 along the six-hold axis are calculated and the structure and properties of endohedral metallofullerenes composed of C60 and Fe are analyzed. The results show:(1) Both new types of single-walled Ti8+4nC12+8n (n = 0, 1, 2, 3,…) nanotubes based on Met-Car Ti8C12 with C3v and D2d symmetries are stable. The similar sp3 hybridization in carbon but strong sp-d hybridization between carbon and titanium atoms is shown in these tubes.(2) As the length of the two forms of titanium-carbon nanotubes increases, the gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO Gap) shows the semiconductor–conductor transition, and the two infinitely long titanium-carbon nanotubes are metallic.(3) The fictitious quasi-static processes of Fe going into and out from C60 are calculated and the results show: compared with going into C60, Fe escaping from C60 needs overcome the higher energy barrier.(4) The process of Fe going into C60 is divided into three stages: 1) The interaction between Fe and C60 is similar to Van der Waals. 2) The bonds of the five-membered ring of C60 near Fe are broken and Fe forms bonds with the near C atoms. 3) The Fe-C bonds are broken and the bonds of the five-membered ring of C60 are recovered. The interactions between Fe and C60 are similar to Van der Waals and Fe goes into C60. (5) For Fe going out from C60, it goes throught three stages in contrast to the stages described above. For the two processes of Fe going into and out from C60, the highest energy barrier point that the Fe atom needs cross locates inside C60 but shifts toward C60 edge for the quasi-static process of the Fe atom going out from C60.