First-principles investigations of the band structure and optical properties of γ-boron

We investigate the electronic structures, optical properties and perform a population analysis of the high-pressure phase of boron (γ-B28) by the norm-conserving pseudopotential density functional method. We employ the Perdew-Burke-Eruzerhof (PBE) form of the generalized gradient approximation (GGA) with plane-wave basis sets to expand the periodic electron density. The dielectric function and optical property constants including the reflectivity, the absorption coefficient, the refractive index, the electron energy-loss function and the optical conductivity are presented in an energy range from 0 to 22 eV. The calculated optical properties indicate that γ-B28 could be an indirect gap optical material with unique properties. The population analysis suggests that the chemical bonding in γ-B28 has predominantly covalent character and mixed covalent-ionic character.