Abstract
Methodologies based on rolling a sheet of graphene were used to design, program and investigate single and double wall silicon carbide zigzag and armchair nanotubes (SiCNTs). For each combination of models we start by investigating details such as type of conformations, diameters, lengths, energy levels and number of atoms. We are thus able to separate groups of isomers based on these properties. We subsequently made calculations with one hundred single wall and twenty double wall armchair and zigzag SiCNTs using semi-empirical AM1, MNDO, HF and DFT with 3-21g and 6-31g basis sets. The semi-empirical, ab-initio and DFT models indicate similar trends. These results may be of interest for workers with limited computational resources. We investigated the stability between isomers of zigzag and armchair with different geometries. We also investigated the effects of radial and vertical growth of nanotubes on stability, geometries, band gaps and charges. These calculations also indicated that the larger and longer configurations are more stable. The average bond distances with single wall indicated values of ~ 1.70 Â in the center of the tube with variations at the extremities. Analysis of the diameters indicates that the armchair configurations are more symmetric than the zigzag. The analysis of |HOMO-LUMO| indicates variations tending to regions of metallic and semiconductor materials. The Mulliken charges are more symmetric for the armchair configurations. Results of the variation of energy with the double wall indicate similar results as for the single wall nanotubes.
Keywords: DFT, double wall, electrical conductivity, nanotubes, silicon carbide, single wall.
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