【摘 要】
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Theoretical studies on Si-doped armchair carbon nanotubes(CNTs)with various diameters have been performed using the SCF-MO method based on DFT calculations.The geometrical optimization,energy and elec
【机 构】
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Key Laboratory of Energy Sources and Chemical Engineering,School of Chemistry Science and Engineerin
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Theoretical studies on Si-doped armchair carbon nanotubes(CNTs)with various diameters have been performed using the SCF-MO method based on DFT calculations.The geometrical optimization,energy and electronic property are all computed using the Kohn-Sham SCF-MO method.The structures,relative stabilities,electronic and nonlinear optical properties as well as aromaticity of the hybrid CNTs are calculated and compared with those of the pure ones.It is found that the obtained POAV angles of the silicon in the doped tubes are in the range of 21.4-34.6 °,and much larger than those of carbon atoms,due to the strong tendency of sp3 hybridization.According to the results of cohesive energy and Gibbs free energy,the stability of the tubes would be decreased upon the silicon doping.Thin tubes also exhibit small values of defect formation energy,and thus the Si-doping occurs easier in thin CNTs.Also we obtained the quantitative relation about the curvature-dependent formation energies with the equation ΔE=7.11-9.31K.All the doped tubes present smaller Eg than those of the pristine,although the change is not obvious for large tubes.Based on the nonlinear response to electric field,the hyperpolarizability of the tubes has been studied.It is found that the values of hyperpolarizability for doped tubes are dramatically enhanced due to the symmetry-reduce and substitution effects.By doing the nuclear independent chemical shift(NICS)scan in the tube axis,it can be observed that the NICS distributions along tube axis display a parabola shape and the values are increased upon the presence of silicon impurity for CNT(n,n)n≥5.As for the aromaticity at the selected positions,the aromaticity/anti-aromaticity transition is even occurred to these tubes as the silicon is introduced in.
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