Improved calculation of band gap of Sr2Bi2O5 crystal using modified Becke-Johnson exchange potential

The electronic structure of Sr2Bi2O5 is calculated by the scalar-relativistic full potential linearized augmented plane wave (FLAPW+lo) method using the modified Becke-Johnson potential combined with the local density approximation correlation (MBJ-LDA). Both the valence band maximum (VBM) and conduction band minimum (CBM) exist at the Γ-point, indicating that Sr2Bi2O5 is a direct-band-gap material. The band gap is calculated to be 3.17 eV, which is very close to the experimental value. This result is in great contrast to the underestimation based on the GGA calculation. On the other hand, there is only a small difference in the effective masses of holes and electrons photogenerated near the VBM and CBM for the MBJ-LDA and GGA approaches. The optical properties of Sr2Bi2O5 are calculated from the complex dielectric function ε(ω)=ε1(ω)+iε2(ω). A highly polarized peak is observed at 3.5 eV in the ε2(ω) function. Furthermore, the absorption coefficient estimated from the MBJ-LDA is very similar to that from the experimental result.