First‐principle simulations on silicon-doped armchair single‐walled carbon nanotubes of various diameters

This work presented theoretical studies of structures, energies and properties of armchair carbon nanotubes (CNTs) upon the silicon substitutional doping by using first-principle calculations. The doping effects on quantitative description from viewpoint of the pi-orbital axis vector theory, relative stability, defect formation energy, electronic structure, nonlinear optical property and aromaticity of the tubes has been addressed systemically and in details. The obtained pyramidalization angles of the silicon are much larger than those of carbon according to the pi-orbital axis vector analysis. The results of defect formation energy suggest that the Si-doping would be contained easier in small CNTs. A quantitative relation about the curvature-dependent defect formation energy is obtained. The silicon atoms exhibit large distributions for the frontier molecular orbital of doped tubes. As for the nonlinear optical property, the hyperpolarizability of the tubes is dramatically enhanced upon silicon defect. The doping effect on the aromaticity is also studied. It is found that the aromaticity/anti-aromaticity transition is even occurred at the selected positions based on the probe of nuclear independent chemical shift.