First-principles study on electronic structure and optical properties of Ca4Bi6O13 crystal

The electronic structure of Ca4Bi6O13 is calculated by the GGA approach. The valence band maximum and the conduction band minimum of Ca4Bi6O13 are located at Gamma-point. This means that Ca4Bi6O13 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 Ca4Bi6O13 are calculated from spectral dependence of the complex dielectric function, epsilon(omega)=epsilon(1)(omega)+i epsilon(2)(omega). A highly polarized peak is observed below 3.6 eV in epsilon(2)(omega) function. (C) 2012 Elsevier Ltd. All rights reserved.