Electronic structure of photoresponsive Ag₆M₂O₇ (M = Si, Ge)

抄録

The electronic structures of Ag₆M₂O₇ (M = Si, Ge) are investigated by the scalar-relativistic full potential linearized augmented plane wave plus local orbital (FLAPW+lo) method using the modified Becke-Johnson (MBJ) potential combined with the local density approximation (LDA) correlation. For Ag₆M₂O₇ (M = Si, Ge), the valence band maximums (VBM) are approximately located at the X (Si) or A (Ge) and the conduction band minimums (CBM) at the Γ both, indicating that Ag₆M₂O₇ are an indirect energy gap material. The fundamental band gaps of Ag₆Si₂O₇ and Ag₆Ge₂O₇ are calculated to be 1.69 and 1.42 eV, respectively, in the MBJ-LDA calculation. The results are a remarkably contrast to the underestimation based on the generalized gradient approximation (GGA) calculation. On the other hand, there is no distinct difference in the effective masses of photogenerated holes and electrons near the VBM and CBM between MBJ-LDA and GGA approaches. The optical properties of Ag₆M₂O₇ (M = Si, Ge) are contemplated from spectral dependence of the complex dielectric function, ε (ω) = ε₁ (ω) + iε₂ (ω).