A Hybrid Density Functional Study of Zigzag and Chiral Si Nanotubes
First principles calculations have been performed to study the electronic and geometric structures of zigzag and chiral silicon nanotubes and compared with the properties of armchair silicon nanotubes. The finite cluster approach with dangling bonds saturated with hydrogen atoms has been used. The theoretical formalism used is the hybrid density functional theory incorporating Hartree-Fock (HF) exchange with the density functional theory (DFT) exchange-correlation functional. In particular, we have used Becke's three parameter with the exchange-correlation functionals of Lee, Yang, and Parr (B3LYP) hybrid functional and the Los Alamos pseudopotential with the associated basis set LANL2DZ as implemented in the Gaussian 03 suite of programs. For silicon, the 1s, 2s, and 2p electrons have been represented by core potentials and the remaining electrons as valence states. A detailed comparison of the structures and stabilities of the nanotubes has been performed and the dependence of the electronic band gaps on the respective tube diameters has been investigated. We have also compared our results with other results published in the literature. Si—Si bond length alternation in SiNTs is more pronounced in SiNTs than that in CNTs, indicating a strong tendency for bond delocalization in Si nanotubes. Also as the number of Si atoms and tube diameter increases, the binding energy per atom for armchair nanotubes approaches saturation value. The band gaps of all the different nanotubes that we have studied vary from 0.129 eV (chiral 6, 2) to 1.159 eV (chiral 6, 3). We infer that some chiral SiNTs can possibly indicate metallic behavior. The Mulliken charge analysis shows that zigzag structures has predominantly ionic bonding while armchair and some of the chiral structures are covalently bonded.
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Document Type: Research Article
Publication date: 2008-04-01
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- Journal of Computational and Theoretical Nanoscience is an international peer-reviewed journal with a wide-ranging coverage, consolidates research activities in all aspects of computational and theoretical nanoscience into a single reference source. This journal offers scientists and engineers peer-reviewed research papers in all aspects of computational and theoretical nanoscience and nanotechnology in chemistry, physics, materials science, engineering and biology to publish original full papers and timely state-of-the-art reviews and short communications encompassing the fundamental and applied research.
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