All calculations were performed using Density Functional Theory (DFT) within periodic boundary conditions through the Vienna Ab Initio Simulation Package (VASP). Using the projectoraugmented wave (PAW) method, scalar-relativistic pseudopotentials were employed to describe the interaction between core and valence electrons. Unless otherwise specified, the rangeseparated screened hybrid DFT functional of Heyd, Scuseria and Ernzerhof (HSE06) was used for all calculations, along with the D3 dispersion correction of Grimme et al. using the zero-damping function, to account for dispersion forces. To account for relativistic effects, spin-orbit interactions were included (HSE06+D3+SOC) in all total energy, electronic and optical calculations. The ionic dielectric response was calculated using linear response theory under finite electric fields (with the HSE06+D3 functional).