Browsing by Author "Jang, Y. -R."
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Item Open Access Hydrogen storage capacity of Ti-doped boron-nitride and B Be-substituted carbon nanotubes(American Physical Society, 2007) Durgun, Engin; Jang, Y. -R.; Çıracı, SalimWe investigate the hydrogen absorption capacity of two tubular structures, namely, B Be -substituted single-wall carbon nanotube (SWNT) and Ti covered single-wall boron nitride nanotube (SWBNT) using first-principles plane wave method. The interaction of H2 molecules with the outer surface of bare SWBNT, which is normally very weak, can be significantly enhanced upon functionalization by Ti atoms. Each Ti atom adsorbed on SWBNT can bind up to four H2 molecules with an average binding energy suitable for room temperature storage. While the substitution process of Be atom on SWNT is endothermic, the substituted Be strengthens the interaction between tube surface and H2 to hold one H2 molecule. © 2007 The American Physical Society.Item Open Access Structural, electronic, and magnetic properties of 3d transition metal monatomic chains: First-principles calculations(American Physical Society, 2008) Ataca, C.; Cahangirov, S.; Durgun, Engin; Jang, Y. -R.; Çıracı, SalimIn this paper we investigated structural, electronic, and magnetic properties of 3d (light) transition metal atomic chains using first-principles pseudopotential plane-wave calculations. Infinite periodic linear, dimerized linear, and planar zigzag chain structures, as well as their short segments consisting of finite number of atoms have been considered. Like Cu, the periodic, linear chains of Mn, Co, and Ni correspond to a local shallow minimum. However, for most of the infinite periodic chains, neither linear nor dimerized linear structures are favored; to lower their energy the chains undergo a structural transformation to form planar zigzag and dimerized zigzag geometries. Dimerization in both infinite and finite chains is much stronger than the usual Peierls distortion and appears to depend on the number of 3d electrons. As a result of dimerization, a significant energy lowering occurs which, in turn, influences the stability and physical properties. Metallic linear chain of vanadium becomes half-metallic upon dimerization. Infinite linear chain of scandium also becomes half-metallic upon transformation to the zigzag structure. An interplay between the magnetic ground state and the atomic as well as the electronic structure of the chain has been revealed. The end effects influence the geometry, the energetics, and the magnetic ground state of the finite chains. Structure optimization performed using noncollinear approximation indicates significant differences from the collinear approximation. Variation of the cohesive energy of infinite- and finite-size chains with respect to the number of 3d electrons is found to mimic the well-known bulk behavior. The spin-orbit coupling of finite chains is found to be negligibly small.