Density functional theory (DFT) calculations were performed using the projector augmented wave method as implemented in the Vienna ab initio simulation package (VASP). The experimental crystal structure was used as a starting point. The geometry was relaxed using the hybrid functional HSE06 with the inclusion of the Grimmes D3 dispersion correction, which is needed to accurately model vacancy-ordered perovskites. Band structure, density of state, and optical calculations were performed with the HSE06 functional with the inclusion of spin-orbit coupling (SOC) due to the presence of heavy-atom elements. The plane-wave cutoff energy (450 eV) and k-mesh density (2×2×2 Monkhorst-Pack grid for the primitive cell) were converged to a total energy difference of 1 meV/atom. The plane-wave cutoff energy was increased to 500 eV during relaxations which allowed volume to change to avoid Pulay stress effects. Visualization and analysis of the electronic structure utilized the effmass, sumo, and PolaronMobility 55 packages.