Carbon Nanoarch Encapsulating Fe Nanowire on Ni (111)

We investigate the stable structures of Fe-filled single-walled carbon nanotubes (SWNTs) on Ni(111), using density functional theory calculations. We find stable geometries and electronic states for the nanotube on Ni(111). We propose the possibility that the C-C bonds of carbon nanotube are broken by Fe wire and Ni surface. That is, when Fe-filled SWNT(3, 3) adsorb on Ni(111) surface, SWNT transforms into arch-like structure.Comment: 13 pages, 6 figures, submitted to Japanese Journal of Applied Physics 22 April 2005. submitted to Japanese Journal of Applied Physics 22 April 200

A DFT+U study on the contribution of 4f electrons to oxygen vacancy formation and migration in Ln-doped CeO2

Rare-earth doped form, ceria (CeO2) is of interest as a potential candidate for solid oxide fuel cells (SOFCs) because of its relatively high oxygen ion conductivity at temperatures below 600 {\deg}C. At the present time, computational chemistry has reached a certain maturity which allows prediction of materials properties that are difficult to observe experimentally. However, understanding of the roles of dopants on the oxygen ion conduction in CeO2 is still incomplete for quantitatively reliable analysis due to strong electron correlation of 4f electrons. In this study, density functional theory calculations with Hubbard U corrections are conducted to discuss ionic/covalent interactions in rare-earth-doped CeO2 and their consequences to oxygen ion conduction. The study suggests that the variable occupancy of empty 4f orbitals is important typically for early Ln elements to produce the covalent interactions that essentially affect formation and migration of oxygen vacancies. This finding is important in understanding the factors responsible for oxygen ion diffusion in doped CeO2.Comment: 22 pages, 9 main figures, 1 main table, 8 supporting information figures and 1 supporting information tabl

H_2 Dissociative Adsorption at the Armchair Edges of Graphite

We investigate and discuss how hydrogen behaves at the edges of a graphite sheet, in particular the armchair edge. Our density functional theory-based calculations results show that, in contrast to the zigzag edge [cf., e-J. Surf. Sci. Nanotech. 2 (2004) 77], regardless of orientation, there is an activation barrier hindering H_2 dissociation at the armchair edges. And once they do get dissociatively adsorbed at the armchair edges, we find that it would be extremely hard to desorb the H from their adsorption sites at the armchair edges. Furthermore, we also found that, consistent with our earlier conclusions [cf., J. Phys. Soc. Jpn. 72 (2003) 1867], it is unlikely that we would find a whole H_2 in between plain graphite sheets.Comment: 4 pages, 5 figures, preprin