Density Functional Theory (DFT) calculations employed in this study are in general agreement with many of the experimentally measured properties. The calculated band gap (1.43 eV, HSE06+SOC) is lower than the experimental optical gap (1.86(1) eV) determined from absorption spectroscopy; however, this is reasonable given the disorder present in the experimental crystal structure. The high-frequency dielectric permittivity calculated from DFT (2.81-3.1) closely resembles the real part of the dielectric permittivity measured at 9 GHz (2.61); the static dielectric permittivity calculated by DFT (22.15) is significantly higher, which suggests the presence of very slow (<< 9 GHz) ion dynamics in the material. However, two key differences require further discussion: the polaron mobility (Hellwarth model, Table ) vs. the carrier mobility from TRMC (Table ) and the observed photoluminescence vs. the electronic band structure calculations.