The relationship between the structure and the properties of a drug or material is a key concept of chemistry. Knowledge of the three-dimensional structure is considered to be of such...

The transport properties, work functions, electronic structure, and structural stability of boron nanotubes with different lattice structures, radii, and chiralities are investigated theoretically. As the atomic structure of boron nanotubes and the related sheets is still under debate, three probable structural classes (nanotubes derived from the α-sheet, the buckled triangular sheet, and the distorted hexagonal sheet) are considered. For comparison with recent transport measurements [J. Mater. Chem. 2010, 20, 2197], the intrinsic conductance of ideal nanotubes with large diameters (D ≈ 10 nm) is determined. All considered boron nanotubes are highly conductive, irrespective of their lattice structures and chiralities, and they have higher conductivities than carbon nanotubes. Furthermore, the work functions of the three sheets and the corresponding large-diameter nanotubes are determined. It is found that the value of the nanotubes obtained from the α-sheet agrees well with the experiment. This indirectly shows that the atomic structure of boron nanotubes is related to the α-sheet. The structural stability of nanotubes with diameters > 2 nm approaches that of the corresponding boron sheets, and α-sheet nanotubes are the most stable ones. However, for smaller diameters the relative stabilities change significantly, and for diameters < 0.5 nm the most stable structures are zigzag nanotubes of the buckled triangular sheet. For structures related to the distorted hexagonal sheet the most stable nanotube is discovered to have a diameter of 0.39 nm.

We present the results of our recent parametrization of the boron−boron and boron−hydrogen interactions for the self-consistent charge density-functional-based tight-binding (SCC-DFTB) method. To evaluate the performance, we compare SCC-DFTB to full density functional theory (DFT) and wave-function-based semiempirical methods (AM1 and MNDO). Since the advantages of SCC-DFTB emerge especially for large systems, we calculated molecular systems of boranes and pure boron nanostructures. Computed bond lengths, bond angles, and vibrational frequencies are close to DFT predictions. We find that the proposed parametrization provides a transferable and balanced description of both finite and periodic systems.

We show that charge doping can induce transitions between three distinct adsorbate phases in hydrogenated and fluorinated graphene. By combining ab initio, approximate density functional theory and tight binding calculations we identify a transition from islands of C 8 H 2 and C 8 F 2 to random adsorbate distributions around a doping level of ±0.05 e/Catom. Furthermore, in situations with random adsorbate coverage, charge doping is shown to trigger an ordering transition where the sublattice symmetry is spontaneously broken when the doping level exceeds the adsorbate concentration. Rehybridization and lattice distortion energies make graphene which is covalently functionalized from one side only most susceptible to these two kinds of phase transitions. The energy gains associated with the clustering and ordering transitions exceed room temperature thermal energies.