Electronic structure and optical properties of the B12O2 crystal

The electronic structure and the optical properties of the icosahedral B12O2 crystal are studied by means of first-principles calculations. The results are compared with the other B-12-based compounds with the same rhombohedral crystal structure. B12O2 is a semiconductor with a direct band gap of about 2.40 eV at Z. It is shown that intericosahedral bonding is stronger than the intraicosahedral bonding in B12O2. There is no covalent bonding between the O atoms and a net charge transfer from the B-12 icosahedron to the O atoms. From the calculated complex dielectric function and energy-loss function, the static dielectric constant and bulk plasmon frequency in Bi12O2 are estimated To be 3.4 and 26.9 eV, respectively, which are smaller than that of other B-12-based compounds.