ABSTRACT
The achiral and chiral systems, which are, respectively, characterized by the zero and non-zero angle between the central line along x and the edge orientation in terms of the arrangement of carbon hexagons. The former is very useful in the characterization of the essential properties in the individual systems. The first-principles calculations within the density functional theory are useful in fully understanding the essential properties of pristine/H-passivated graphene nanoribbons. The geometric and electronic properties of pristine and hydrogen-passivated armchair graphene nanoribbons are investigated for various widths. The modifications on the tight-binding model are very useful to understand the semiconducting behavior of planar graphene nanoribbons with hydrogen passivation, the strong dependence of energy gap on the edge structure and width. Zigzag graphene nanoribbons exhibit the similar geometric properties and thus the chemical bondings near the boundaries, as observed in armchair ones.
