Origin and nature of the band gap in β-FeSi2

The recent interest in beta-FeSi2, the semiconductor phase of metallic iron silicides, is related to the nature of its gap. By semiempirical tight-binding calculations we investigate the formation of the gap and the changes in the cohesion energy when the original calcium-fluorite structure (hulk unstable and metallic) is distorted into the beta phase. We find out that the latter corresponds to an indirect semiconductor, but minor deformations of the structure turn the gap into a direct one.