Simulations of density of states of different chirality carbon nanotubes

The structure of a Single Wall Carbon Nanotube (SWCNT) is specified by a chiral vector(Ch=(n,m)). The electronic properties of SWCNTs strongly depend upon the tube diameterand chirality (given by the chiral indices m and n). SWCNT?s are either metallic orsemiconducting depending on their structural parameters.Tight-Binding Molecular Dynamics is successful in studying the structural, dynamical, andelectronic properties of SWCNTs. The traditional TB solves the Schrödinger equation bydirect matrix diagonalization and uses the simulation time in cubic scaling with the respect tothe number of atoms (O ( N 3 )). The Order N (O(N)) methods solve for the band energy in realspace and make the approximation that only the local environment contributes to the bonding,and hence the band energy of each atom. In this case, the run time would be linearly scaledwith respect to the number of atoms.In this study we use O(N) TBMD method in parallel computation to investigate electronicproperties of SWCNT?s with varying chiralities from (2,2) to (30,0). This thesis has beenmade at Yıldız Technical University Carbon Nanotube Simulation Laboratory. We calculatedthe electronic density of state (eDOS), fermi energy level and band structure energy of eachtube. Using eDOS graphs, we defined the general rules for determining whether SWCNT ismetallic or semiconducting. We showed that based on the chiral indices (n,m): the tube ismetallic when n=m; tube is a small-gap semiconductor when n-m=3i, where i is a nonzerointeger. All other combinations of (n,m) give true semiconductors. The band gap of asemiconducting SWCNT is approximately inversely proportional to the tube diameter. Weestimated the band gaps of semiconducting SWCNTs and compared them with the availabletheoretical results. Temperature effect on electronic properties is shown using energy bandgaps, electronic density of states and fermi levels at two different temperature.Keywords: Carbon Nanotubes, Electronic properties of CNT, Density of states, Band gapenergy, Molecular Dynamics, Tight-Binding method, Parallel Environments, Order N, FermiLevelJURY:1.Prof. Dr. Gülay DERELİ (Supervisor) Date:21.06.20062.Doç. Dr. Sondan DURUKANOĞLU Page:783.Yrd. Doç. Dr. Orhan ÖZDEMİR