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The interlayer π-π interaction between finite-size models of graphene sheets was investigated by using a density functional theory method, augmented with an empirical R-6 term for the description of long-range dispersive interaction; these were calibrated by studying the π-π interaction between various benzene dimer configurations and comparing the results with previous calculations. For stacked bilayers (dimers) and multilayers of polyaromatic hydrocarbons, which serve as molecular models of graphene sheets, we found that binding energies and energy gaps are strongly dependent on their sizes, while the stacking order and the number of stacked layers have a minor influence. The remarkably broad variation of the energy gap, ranging from 1.0 to 2.5 eV, due mainly to variation of the model size, suggests the potential of broadband luminescence in the visible range for carbon-based nanomaterials that have π-π interacting. [ABSTRACT FROM AUTHOR]

A promising material for hydrogen storage at room temperature–Al doped graphene is proposed theoretically by using density functional theory calculation. Hydrogen storage capacity of 5.13 wt % is predicted at T=300 K and P=0.1 GPa with an adsorption energy Eb=-0.260 eV/H2. This is close to the target specified by U.S. Department of Energy with a storage capacity of 6 wt % and a binding energy of -0.2 to -0.4 eV/H2 at ambient temperature and modest pressure for commercial applications. It is believed that the doped Al alters the electronic structures of both C and H2. The bands of H2 overlapping with those of Al and C simultaneously are the underlying mechanism of hydrogen storage capacity enhancement. [ABSTRACT FROM AUTHOR]

The interactions of a hydrogenated silicon nanodot, Si35H36, containing surface SiH and SiH2 surface hydrides, with three representative small polar molecules, ethanol, NH3, and H2O were comparatively studied using a self-consistent charge density-functional tight-binding method, complemented by an empirical van der Waals force correction. The binding energy of ethanol with the hydrogenated silicon dot was determined to be 0.39–0.78 eV with a positive sign, indicating that this adsorption process is endothermic and thermodynamically unfavorable. In contrast, the binding energies of H2O and NH3 were found to be about 0.15–0.53 eV with a negative sign, revealing exothermic and thermodynamically favorable reactions. Interestingly, these adsorptions are facilitated by H...H attraction, rather than by H...O or H...NH-bonding. The binding is mostly electrostatic and physical, with very little charge transfer occurring. All these adsorptions result in relatively small redshifts in optical absorption and emission spectra, according to additional time-dependent calculations, with little change in the IR peak position of their adsorbents and an almost perfect silicon surface. [ABSTRACT FROM AUTHOR]

We show here that an economic basis set can describe nucleic acid base pairs involving the hydrogen bond interactions in density functional calculations. The economic basis set in which the polarization function is added only to oxygen and nitrogen atoms of strong electronegativity can predict reliable geometric structures and dipole moment of nucleic acid base pairs, comparable to those obtained from the basis set of 6-31G* in B3LYP calculations. Combining single point calculations with the standard basis set on the geometric structures optimized by the economic basis set, the present approach has predicted accurate natural bond orbital charge, binding energy, electronegativity, hardness, softness, and electrophilicity index. The principle for basis selection presented in this study can be regarded as a general guideline in the computation of large biological systems with considerably high accuracy and low computational expense. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]

Hydrogen storage by carbon nanotubes (CNTs) is a challenging issue still in debate. Using an approximate density functional method augmented with a van der Waals dispersion term, we have shown that there are binding maxima for H2/single-walled carbon nanotube (SWCNT) complexes at (5, 5) and (8, 0) tubes for armchair and zigzag CNTs, respectively, with binding energies around three times as large as that of H2 on graphene surface. We predict that SWCNTs with diameters of 6–7 Å are energetically optimal candidates for physisorption of molecular hydrogen. [ABSTRACT FROM AUTHOR]

We investigated [0001] bare and functionalized gallium nitride (GaN) nanowires by using the density-functional theory. Passivation of GaN nanowires with various functional groups (H, NH2, OH, and SH) show distinct electronic properties. We found that the band gap for the nanowires with partial surface coverage is dependent on the coverage ratio and adsorption sites. In view of the importance of surface states to the properties of nanowires, we suggest that the electronic and optical properties can be modulated by controlling the surface states of nanowires by functionalization. [ABSTRACT FROM AUTHOR]

The authors employ density functional theory within the generalized-gradient approximation to investigate infinitely long [0001] ZnO nanowires. The authors report on atomic relaxations, formation energies, and electronic structure of bare and hydrogen passivated ZnO wires with triangular cross sections. The authors find that surface reconstruction plays an important role in stabilizing the nanowires. The authors have shown that the band gap can be tuned by changing the wire diameter and by passivating with hydrogen. While bare and completely passivated wires are semiconducting, wires with intermediate hydrogen passivation exhibit metallic behavior. [ABSTRACT FROM AUTHOR]

The structure and electronic properties of the (√13 x √13)R13.9° and (2√ x 2√3)R30° ordered phases of C60 on the Pt(111) surface are investigated using combined dynamic low-energy electron diffraction and density functional theory (DFT) calculations. The two phases have the same local adsorption structure, while they are predicted by DFF calculations to exhibit very different electronic structures due to their different inter-C60 orientations and distances. This result demonstrates the structural tuning of electronic properties for molecular films or junctions composed of the same materials. [ABSTRACT FROM AUTHOR]