Density Functional Theory

Carbon nanomaterials have attracted much attention because they are candidates for post-silicon mate-rials. Since carbon nanotubes (CNTs) were detected and graphene was isolated from graphite, compre-hensive studies have been carried out with the aim of exploiting the properties of these materials. In this study, by using first principles calculations, we study the interlayer distance of the two-layer graphene and atomic hydrogen adsorption in graphenes and CNTs. We first study layer distance of the two-layer graphene. We use a recently developed van der Waals density functional theory (VDWDFT) as well as the local density approximation (LDA). Both methods give successful results for graphite; i.e. the calculated interlayer distances are comparable with the experimental value. We find that the interlayer distance of the two-layer graphene is close to that of graphite. We also find that the AA stacking structure of the two-layer graphene has higher energy than that of the AB stacking one and the layer distance of the AA stacking is larger than that of the AB stacking. It is thus suggested that the interlayer distance becomes somewhat large when the stacking deviates from the AB stacking. Next, we study hydrogen monomers and dimers in graphene, the armchair edge (5, 5) carbon nan-otube (CNT), and the zigzag edge (10, 0) CNT because the presence of hydrogen atoms could chang