Electronic structure of alkali-metal fluorides, oxides, and nitrides: density-functional calculations including self-interaction corrections

The recently synthesized compound Na3 N has experimentally been shown to be semiconducting much in contrast to the outcome of standard density-functional theory calculations which find Na3 N to be metallic. To address this obvious contradiction, we have systematically investigated the electronic structure of Na3 N by density-functional calculations employing self-interaction-corrected pseudopotentials which have been shown before to yield results in much better agreement with experiment than standard local-density calculations. To assess the usefulness of such pseudopotentials for a broader class of related materials, we have carried out, in addition, a comparative ab initio study of the electronic structure of the nine alkali-metal fluorides MF, oxides M2 O, and nitrides M3 N with M=Li, Na, and K. We arrive at valence and conduction bands that are in good agreement with the restricted results available in the literature from calculations going beyond the local-density approximation and from experiment. In particular, Na3 N turns out to be clearly semiconducting, as observed in experiment.