Browsing by Author "Dereli, G."

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Citation - Scopus: 10
O(N) Algorithms in Tight-Binding Molecular-Dynamics Simulations of the Electronic Structure of Carbon Nanotubes
(2003) Dereli, G.; Özdoǧan, C.
The O(N) and parallelization techniques have been successfully applied in tight-binding moleculardynamics simulations of single-walled carbon nanotubes (SWNT's) of various chiralities. The accuracy of the O(N) description is found to be enhanced by the use of basis functions of neighboring atoms (buffer). The importance of buffer size in evaluating the simulation time, total energy, and force values together with electronic temperature has been shown. Finally, through the local density of state results, the metallic and semiconducting behavior of (10 X 10) armchair and (17 X 0) zigzag SWNT's, respectively, has been demonstrated.
Structural stability and energetics of single-walled carbon nanotubes under uniaxial strain
(2003) Özdoğan, Cem; Özdoğan, Cem; 40569; Ortak Dersler Bölümü
A (10x10) single-walled carbon nanotube consisting of 400 atoms with 20 layers is simulated under tensile loading using our developed O(N) parallel tight-binding molecular-dynamics algorithms. It is observed that the simulated carbon nanotube is able to carry the strain up to 122% of the relaxed tube length in elongation and up to 93% for compression. Young's modulus, tensile strength, and the Poisson ratio are calculated and the values found are 0.311 TPa, 4.92 GPa, and 0.287, respectively. The stress-strain curve is obtained. The elastic limit is observed at a strain rate of 0.09 while the breaking point is at 0.23. The frequency of vibration for the pristine (10x10) carbon nanotube in the radial direction is 4.71x10(3) GHz and it is sensitive to the strain rate.
Citation - WoS: 9
Citation - Scopus: 11
Thermal stability of metallic single-walled carbon nanotubes: an O(N) tight-binding molecular dynamics simulation study
(Iop Publishing Ltd, 2007) Dereli, G.; Özdoğan, Cem; Suengue, B.; Oezdogan, C.; 10524; 188507; Ortak Dersler Bölümü
Order(N) tight-binding molecular dynamics (TBMD) simulations are performed to investigate the thermal stability of ( 10, 10) metallic single-walled carbon nanotubes (SWCNTs). Periodic boundary conditions (PBCs) are applied in the axial direction. The velocity Verlet algorithm along with the canonical ensemble molecular dynamics (NVT) is used to simulate the tubes at the targeted temperatures. The effects of slow and rapid temperature increases on the physical characteristics, structural stability and the energetics of the tube are investigated and compared. Simulations are carried out starting from room temperature and the temperature is raised in steps of 300 K. The stability of the simulated metallic SWCNT is examined at each step before it is heated to higher temperatures. The first indication of structural deformation is observed at 600 K. For higher heat treatments the deformations are more pronounced and the bond-breaking temperature is reached around 2500 K. Gradual ( slow) heating and thermal equilibrium ( fast heating) methods give the value of radial thermal expansion coefficient in the temperature range between 300 and 600 K as 0.31 x 10(-5) and 0.089 x 10(-5) K-1, respectively. After 600 K, both methods give the same value of 0.089 x 10(-5) K-1. The ratio of the total energy per atom with respect to temperature is found to be 3 x 10(-4) eV K-1.