Boron, Nitrogen, And Quasi-planar Four-coordinate Carbon-doped Carbon Nanotube Structure And The Nature Of Theoretical Research

Three kinds of nanotubes which were doped with boron and nitrogen atoms, as well as multi-qusai-planar tetracoordinate carbon atoms (mqptC):B-and N-doped (4,4) and (8,0) carbon nanotubes BxCyNx(x,y>0) with aperiodic strutcures; BC2N(4,4) and BC2N(8,0) nanotubes with periodic structures; boron carbon nanotubes with mqptC, have been investigated by using density functional theory (DFT). The main contents can be divided into three parts as follows:1. The B-and N-doped (4,4)j and (8,0)j (j=3-5) carbon nanotubes, BCyN (y= 1-4,6 and 8), B3CyN3 (y=2 and 4), B2CN2, as well as BN nanotubes have been investigated using B3LYP/6-31G* method. The lowest energy structures of BxCyNx nanotubes of doped (8,0)j carbon nanotubes indicate that the B and N atoms prefer to dope (8,0)j carbon nanotubes from bottom to top layer by layer. When the number of BN layers of doping (4,4)j carbon nanotubes equal to j-1, the B and N atoms are situated in the middle possitions of BxCyNx nanotube and carbon atoms locate on its top and bottom. Otherwise, the doped ways of B- and N- doped (4,4)j carbon nanotubes are similar to those of (8,0)j. Caculated energy gaps of (4,4)j and (8,0)j (j=3-5) BN nanotubes are between 5.51 and 6.38eV, which are in goode agreement with the experimental energy gap of 5.5 eV. In addition, the energy gaps of BC2N and BCN nanotubes are consistent with the previous theoretical and experimental results. The variety of energy gaps of BxCyNx nanotubes of doped (4,4)j and (8,0)j (j=3-5) carbon nanotubes follow the same trend. Howerver, the energy gaps of doped (4,4)j carbon nanotubes are greater than those of doped (8,0)j ones.2. C(4,4) nanotubes with seven kinds of periodic length, as well as BC2N(4,4) and BC2N(8,0) nanotubes with four kinds of periodic length were constructed. Within the Dmol3 in MS program, the structures of C(4,4)j (j=1-7), BC2N(4,4)j and BC2N(8,0)j (j=2,4,6,8) nanotubes were optimized by GGA/BLYP method in combination with DND basis set, in addition, the band structure and density of states were computed. The results show that the C(4,4) nanotubes are metallic, and the band gap increase with the increase of periodic length, while BC2N(4,4)j and BC2N(8,0)j (j=2,4,6,8) nanotubes reveal semiconductor, however, the band gaps of these nanotubes have significant change with the diffence of the periodic length. Thus, the electronic properties of C(4,4) and BC2N nanotubes can be adjusted by changing the periodic length.3. The structures and HOMO-LUMO gaps of mqptC-doped C(6,0)j nanotubes BC(6,0,i,j) (i=1,2 j=2-4) were carried out at B3LYP/6-31G* level. Calculated results indicate that carbon layers are favorable to locate the above of the boron atoms of C2ptCB2 unit in BC(6,0,i,j) (i=1,2 j=2-4) nanotubes. The structures of C(6,0) nanotubes units in BC(6,0,i,0) nanotubes have no significant variation. Moreover, the mqptC-doped C(6,0)j nanotubes BC(6,0,i,j) contain ten-membered ring windows. The energy gaps of BC(6,0,1,j) (j=2-4) nanotubes monotone decrease with the increase of number of the carbon atoms layers. But the energy gaps of BC(6,0,2,j) (j=2-4) nanotubes gradually increase and then keep invariant. The energy gaps of BC(6,0,1,j) (j=2-4) nanotubes are greater than those of BC(6,0,2,j) (j=2-4) nanotubes.