Structure and Stability of Boron Nitrides: Isomers of B12N12

Modelling nano-clusters and nucleation

We review the growing role of computational techniques in modelling the structures and properties of nano-particulate oxides and sulphides. We describe the main methods employed, including those based on both electronic structure and interatomic potential approaches. Particular attention is paid to the techniques used in searching for global minima in the energy landscape defined by the nano-particle cluster. We summarise applications to the widely studied ZnO and ZnS systems, to silica nanochemistry and to group IV oxides including TiO(2). We also consider the special case of silica cluster chemistry in solution and its importance in understanding the hydrothermal synthesis of microporous materials. The work summarised, together with related experimental studies, demonstrates a rich and varied nano-cluster chemistry for these materials.

Silicon carbide nanostructures: a tight binding approach

A tight-binding model Hamiltonian is newly parametrized for silicon carbide based on fits to a database of energy points calculated within the density functional theory approach of the electronic energy surfaces of nanoclusters and the total energy of bulk 3C and 2H polytypes at different densities. This TB model includes s and p angular momentum symmetries with nonorthogonal atomic basis functions. With the aid of the new TB model, minima of silicon carbide cagelike clusters, nanotubes, ring-shaped ribbons, and nanowires are predicted. Energetics, structure, growth sequences, and stability patterns are reported for the nanoclusters and nanotubes. The band structure of SiC nanotubes and nanowires indicates that the band gap of the nanotubes ranges from 0.57 to 2.38 eV depending on the chirality, demonstrating that these nanotubes are semiconductors or insulators. One type of nanowire is metallic, another type is semiconductor, and the rest are insulators.

Bonding analysis and stability on alternant B16N16 cage and its dimers

Bonding analysis is performed on alternant B(16)N(16) cage based on a combined study of DFT with NBO method. The main feature of such analysis is the separation of bonding structure into two components: sigma skeleton and pi bond system. Each component is further decomposed into contributions from various NBOs, thus we obtain the details of bonding interactions of every BN unit. Based on these results, relative stability of four covalent dimers of B(16)N(16) is predicted and this prediction is verified by DFT calculations. So the possibility of forecasting properties of oligomers just from analysis on monomer is highlighted in this way.

A Family of Stable Silica Fullerenes with Fully Coordinated Structures

Theoretical electronic structure techniques have become an indispensable and powerful tool for predicting molecular properties and designing new materials. The discovery of C(60) opened a challenging field in nanoscale materials science, and since then people have been looking for its inorganic analogues. On the basis of the B3LYP/6-31G(d) calculations, here we provide theoretical evidence for a family of stable silica fullerenes with fully coordinated structures, which exhibit highly structural and energetic stabilities, very large energy gaps, and extremely good resistibilities to breakdown of the insulating capability in an applied electric field. Our calculations indicate that the discrete silica fullerenes are a possible polymorph of silica and can be synthesized under some conditions. They are expected to find novel applications in silica-based molecular devices. The present results may provide an aid in the experimental design for controllably producing desired silica clusters.

Boron nitride cages from B12N12 to B36N36: square-hexagon alternants vs boron nitride tubes

The structures and stabilities of square-hexagon alternant boron nitrides (Bx Nx , x=12-36) vs their tube isomers containing octagons, decagons and dodecagons have been computed at the B3LYP density functional level of theory with the correlation-consistent cc-pVDZ basis set of Dunning. It is found that octagonal B20N20 and B24N24 tube structures are more stable than their square-hexagon alternants by 18.6 and 2.4 kcal mol(-1), respectively, while the square-hexagon alternants of other cages are more stable. Trends in stability as a function of cluster size are discussed.