and Sc2Si2Te6 using HSE06+SOC. The difference in A-site cations markedly affects the band structure. Sb2Si2Te6 exhibits a direct band gap of 0.48 eV, with both the CBM and VBM located at the Z point and this value is close to the experimental optical gap (~ 0.6 eV). In contrast, Sc2Si2Te6 exhibits an indirect band gap of 0.92 eV, where the VBM is located at the Γ point and the CBM is at the Σ point along the L-B path in reciprocal space. This is not a high-symmetry k-point, resulting in significantly increased k-point degeneracy at the conduction band edge. Sb2Si2Te6 has high electronic band dispersion, which will yield small carrier effective masses and higher carrier mobility. As indicated by the accompanying DOS plots in Figure , the CBM is composed of Sb-5p and Te-5p orbitals in Sb2Si2Te6 and Sc-3d orbitals in Sc2Si2Te6, while the VBM mainly derives from Te-5p orbitals. In Sb2Si2Te6 there is a slight contribution to the VBM from Sb-5s orbitals while there is minimal hybridization with Sc-3d orbitals at the VBM in Sc2Si2Te6, which modifies the Te-p valence band edge.