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Hydrogenated silicenes possess peculiar properties owing to the strong H-Si bonds, as revealed by an investigation using first principles calculations. Various charge distributions, bond lengths, energy bands, and densities of states strongly depend on different hydrogen configurations and concentrations. The competition between strong H-Si bonds and weak sp(3) hybridization dominate the electronic properties. Chair configurations belong to semiconductors, while the top configurations show a nearly dispersionless energy band at the Fermi level. Both the systems display H-related partially flat bands at middle energy and the recovery of low-lying π bands during the reduction of concentration. Their densities of states exhibit prominent peaks at middle energy, and the top systems have a delta-funtion-like peak at E = 0. The intensity of these peaks is gradually weakened as the concentration decreases, providing an effective method to identify the H-concentration in scanning tunneling spectroscopy experiments.

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The geometric and electronic properties of curved armchair graphene nanoribbons without hydrogen atoms are investigated by first-principles calculations. The edge-atom bond length and ground state energy dramatically vary with the arc angle. The zipping or unzipping requirements for energy, arc angle, and interaction distance depend on the ribbon width. The increasing curvatures lead to drastic changes in electronic structures, such as energy gaps, energy dispersions, band-edge states, band mixing, band overlap and state degeneracy. There exist semiconductor-metal transitions during the variation of curvature. These are associated with the contribution of the edge atoms, the competition between the π and σ bonds, and hybridization of the 2p(y) and 2p(z) orbitals. The main features of the energy bands dominate the frequency, height, number, and structure of the prominent peaks in the density of states. The predicted results could be examined by experimental measurements.