Electronic structure of CaB₆

The calcium hexaboride, CaB6, is a typical semiconducting metal hexaboride. Here two self-consistent APW calculations of its electronic energy bandstructure are reported, in the muffin-tin approximation and in the warped muffin-tin approximation. In both calculations, the local-spin-density approximation is used and the relativistic effects are taken into account. The bandstructure of the muffin-tin approximation is semimetallic. The non-muffin-tin corrections in the warped muffin-tin approximation tends to cause a small, direct energy gap between the valence and conduction bands at the X points in the simple cubic Brillouin zone. The magnitude of the energy gap to 0.3 eV, in reasonable agreement with the experimental value, 0.4 eV, suggested by the temperature dependence of the electrical resistivity. The calculated result for the density of states agrees reasonably well with an experimental result for the XPS spectrum.