First-principles study on electronic structure and optical properties of Ca _4Bi _6O _(13) crystal

摘要

The electronic structure of Ca _4Bi _6O _(13) is calculated by the GGA approach. The valence band maximum and the conduction band minimum of Ca _4Bi _6O _(13) are located at Γ-point. This means that Ca _4Bi _6O _(13) is a direct band gap material. The conduction band in the lower energy region is mainly constructed with the admixture of Bi 6p and O 2p. The conduction band in the higher energy region consists of Ca 3d states. The valence band in the lower energy region is mainly formed from Bi 6s states, and the valence band in the upper energy region consists of O 2p states hybridizing with Bi 6s and 6p states. The optical properties of Ca _4Bi _6O _(13) are calculated from spectral dependence of the complex dielectric function, ε(ω)=ε _1(ω)iε _2(ω). A highly polarized peak is observed below 3.6 eV in ε _2(ω) function.