Electronic band structures and and independent-particle optical absorption spectra were initially calculated with the HSE06 hybrid DFT functional, including spin-orbit coupling effects (HSE06+SOC) due to the presence of heavy-atom elements (see Results and Section S4). For density of states (DOS) and optical calculations, the k-point mesh for the primitive unit cell was increased to 8 × 8 × 8 (reciprocal space density of 0.12 Å-1 ), and the tetrahedron smearing method was used. The number of virtual states in the optical calculations was increased using vaspup2.0 77 until the high-frequency dielectric constant ε ∞ was converged to a precision of 0.01. Electronic band structure diagrams were generated using sumo. Carrier effective masses were determined using non-parabolic fitting of the band edges through the effmass 81 package.