Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals.

We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

Advances in computational studies of energy materials.

We review recent developments and applications of computational modelling techniques in the field of materials for energy technologies including hydrogen production and storage, energy storage and conversion, and light absorption and emission. In addition, we present new work on an Sn2TiO4 photocatalyst containing an Sn(II) lone pair, new interatomic potential models for SrTiO3 and GaN, an exploration of defects in the kesterite/stannite-structured solar cell absorber Cu2ZnSnS4, and report details of the incorporation of hydrogen into Ag2O and Cu2O. Special attention is paid to the modelling of nanostructured systems, including ceria (CeO2, mixed Ce(x)O(y) and Ce2O3) and group 13 sesquioxides. We consider applications based on both interatomic potential and electronic structure methodologies; and we illustrate the increasingly quantitative and predictive nature of modelling in this field.