الفهرس 
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Abstract
This thesis represents a theoretical study for pristine heterojunction carbon nanotubes (CNTs), mono-vacancy defected heterojunction CNTs and boron -doped heterojunction CNTs to understand their structures, energies and electronic properties. The thesis consists of six chapters, general conclusions and potential applications of our simulated heterojunction CNTs and finally a list of references.
In chapter I, we write a brief report on carbon, allotropes of carbon, heterojunctions CNTs, types of CNTs; structures and physical properties of them.
In chapter II, we report a short theoretical background about the field of computational physics, starting from the basic electronic problems to the Hartree-Fock (HF) and density functional (DFT) theories. The Gaussian 03W and Gaussian View (4.1) program package have been used.
In chapter III, a literature review on electronic and geometric properties of carbon nanotubes and heterojunctions CNTs is reported.
In chapter IV, we investigate the pristine armchair-armchair heterojunction carbon nanotubes (CNTs), mono-vacancy defected armchair-armchair heterojunction CNTs and boron -doped heterojunction armchair-armchair CNTs to obtain their geometrical structures, energy per carbon atom, energy gaps, HOMO-LUMO energy levels, and formation energy, dipole moment. Also, the alpha- , beta- and total density of states , in addition to the energy levels are plotted and analyzed for all armchair-armchair heterojunction CNTs.
In chapter V, we investigate the pristine zigzag-zigzag heterojunction CNTs, mono-vacancy defected zigzag-zigzag heterojunction CNTs and boron -doped heterojunction zigzag-zigzag CNTs to obtain their geometrical structures, energy per carbon atom, energy gaps, HOMO-LUMO energy levels, and formation energy, dipole moment. Also, the alpha- , beta- and total density of states , in addition to the energy levels are plotted and analyzed for all zigzag-zigzag heterojunction CNTs.
In chapter VI, we investigate the pristine zigzag-armchair heterojunction CNTs, mono-vacancy defected zigzag- armchair heterojunction CNTs and boron -doped heterojunction zigzag- armchair CNTs to obtain their geometrical structures, energy per carbon atom, energy gaps, HOMO-LUMO energy levels, and formation energy, dipole moment. Also, the alpha- , beta- and total density of states , in addition to the energy levels are plotted and analyzed for all zigzag-armchair heterojunction CNTs.
Finally, a general conclusion on the geometrical and electronic properties of pure and defected heterojunction CNTs is given beside to the potential applications which have been found for our applied heterojunction CNTs.