Equilibrium geometry and electronic structure There is a slight asymmetric distortion of the octahedra in Sc2Si2Te6. The atom colours are Sb: orange, Sc: pink, Si: purple, and Te: blue. Both Sb2Si2Te6 (Figure ) and Sc2Si2Te6 (Figure ) exhibit rhombohedral symmetry (space group R 3 ̅ , No. 148) and consist of ABC-stacked slabs of (Sb/Sc)2Si2Te6, where Sb (Sc) atoms and Si-Si dumbbells are arranged within the slabs (Figure ). Table presents the lattice parameters of the conventional unit cell, optimized using both PBEsol and HSE06 with the D3 dispersion correction. The calculated lattice constants for Sb2Si2Te6 and Sc2Si2Te6 agree well with the experimental measurements with HSE06+D3 showing improved agreement, though with a slight underestimation of the interlayer spacing as expected when neglecting temperature effects. Compared to Sb2Si2Te6, Sc2Si2Te6 exhibits a slight asymmetric distortion of the octahedra, with shorter Sc-Te bond lengths due to the smaller ionic radius of Sc but larger interlayer spacing.