Understanding electronic and optical properties of strontium titanate at both PBE and HSE06 levels

The structural parameters, electronic structure and optical properties of strontium titanate have been investigated by the first-principles. Exchange–correlation effects are treated by the generalized gradient approximation(GGA) employing Perdew–Burke–Ernzerhof (PBE) functional and hybrid density functional Heyd-Scuseria-Ernzerhof(HSE06). The direct-band gaps are equal to 2.06 and 3.73 eV under PBE and HSE06 level, respectively. The indirect-band gaps are equal to 1.67 and 3.33 eV under PBE and HSE06 level, respectively. The optical properties including complex dielectric function, absorption coefficient, refractivity and reflectivity index have been calculated. Meanwhile, the origin of the spectral peaks on the basis of the electronic band structures has been interpreted. (paper)