Accurate full-potential self-consistent linearized augmented-plane-wave (FLAPW) calculations have been carried out for hexagonal boron nitride. The resulting energy-band structure indicates that this material is an indirect-gap insulator and shows the existence of two unoccupied interlayer bands, similar to those found in graphite and graphite intercalation compounds. Chemical bonding is mainly covalent, with a small charge transfer towards the nitrogen atoms. Moreover, model-potential calculations, based on first-principles FLAPW wave functions and potentials, have been used to study slabs of thickness up to 35 layers. Contrary to the case of graphite, our results do not provide evidence of surface states associated with the interlayer bands.

Although generally ascribed to the presence of defects, an ultimate assignment of the different contributions to the emission spectrum in terms of surface states and deep levels in ZnO nanostructures is still lacking. In this work we unambiguously give first evidence that zinc vacancies at the (1010) nonpolar surfaces are responsible for the green luminescence of ZnO nanostructures. The result is obtained by performing an exhaustive comparison between spatially resolved cathodoluminescence spectroscopy and imaging and ab initio simulations. Our findings are crucial to control undesired recombinations in nanostructured devices.

The spontaneous bulk polarization of wurtzite BeO is studied using ground-state first-principles theory. This quantity, which is not accessible when imposing periodic boundary conditions, is obtained with a novel approach based on the supercell method. The calculated macroscopic polarization is ${\mathit{P}}_3$=1.5×${10}^{\mathrm{-}2}$ C/${\mathrm{m}}^2$, and mostly results from the internal crystallographic distortion. No experimental value of ${\mathit{P}}_3$ exists, but the calculated differences in polarization, between different geometries, compare well with available data.

The interaction of water with Si- and C- terminated $\beta \mathrm{\text{−}}\mathrm{S}\mathrm{i}\mathrm{C}\left(001\right)$ surfaces was investigated by means of ab initio molecular dynamics simulations. Irrespective of coverage, varied from $1/4$ to 1 monolayer, we found that water dissociates on the Si-terminated surface, substantially modifying the clean surface reconstruction, while the C-terminated surface is nonreactive and hydrophobic. Based on our results, we propose that STM images and photoemission experiments may detect specific changes induced by water on both the structural and electronic properties of SiC(001) surfaces.