Tight Binding method for carbon nanotubes Essay

Tight Binding method for light speed nano vacuum tubes - Essay ExampleCarbon nanotubes are long, prune cylinders of carbon and have a very broad range of electronic, thermal, and structural properties that change depending on the assorted kinds of nanotube. The chiral vector of the nanotube, B= nR1 + mR2 where R1 and R2 are unit vectors in the two-dimensional hexagonal lattice, and n and m are integers. another(prenominal) important parameter is the chiral angle, which is the angle between quite a little R1.Diameter D = a3 (n2 + nm + m2)/ p ,Where, ac is the distance between neighboring carbon atoms in the flat sheet. The different values of n and m lead to different types of nanotube. They are armchair, zigzag and chiral nanotubes. Armchair nanotubes areformed when n = m and the chiral angle is 30. zag nanotubes are formed when either n =0 or m==0 and the chiral angle is 0. opposite nanotubes, with chiral angles between 0 and 30, are known as chiral nanotubes. The properties of nanotubes are determined by their diameter and chiral angle, both of which depend on n and m.The electronic characteristics of the nanotubes have been done by numerical band organize, the structure of the chemical bonds. is given by the local spatial structure of the orbital. The electronic structure of the nanotube fragments are calculated by SCF-MO-LCAOVmethods. In this method, only valence electrons are taken into account and the three- and four-center integrals are omitted and the distaste of lone electron pairs can be explained. The SCF convergence criterion was 10-8for total-energy changes and 10-5 for charge-density changes between two subsequent cycles. Band structure calculations of n, 0 (n = 6, 7, 8, 9)tubes were performed using the tight-binding Hamiltonian, with a universal rank of first and second nearest-neighbor hopping integrals that reproduce various carbon structures, including graphite. The 2s, 2px, 2py, 2pz, and s* orbital of each carbon atom are used as th e basis set for expressing the tight binding model. The Hamiltonian matrix elements and related parameters are obtained by adjusting the model to fit photoemission band-structure data. The (6, 0) carbon tube seems to have the lowest diameter and are thermodynamically unstable. The bonds at the ends of the nanotube fragments get saturated by hydrogen atoms. The structural unit of the tube is the distorted carbon hexagon. All c-c bonds were assumed to be of the uniform length 1.4 .Page 3The distance between third-neighbor carbon atoms along the tube circumference is 2.39 . The dose group symmetry of the (6, 0) nanotube fragment is determinedby the number N of carbon hexagons along the tube axis. There is a difference between heat of formation of the nanotube fragments, caused by the limit point atoms affect,strongly at the central part of the nanotube fragment. In the above Figure, the dispersion curves of the (n, 0) tubes with n = 6... 11are shown. This tube family splits into thr ee groups. The (3n, 0) tubes have vanishing energy gaps. The gap increases in (3n + 1, 0) and in (3n + 2, 0) tubes. Consequently, (6, 0) and (9, 0) tubes will in all probability show metallic conductivity, similar to graph. In graphite, orbital are represented in carbon nanotubes, the radial tire orbital are analogous to the lone orbital of graphite .This changes the character of the frontier orbital