spectra of the alloyed materials (Figure ,eError! Reference source not found.) despite the naivety of this approach, further demonstrating the molecular aggregate type nature of this family. The validity of this approach here is further demonstrated by comparing the explicitly-computed independent-particle (HSE06+SOC) absorption spectra of the mixed-cation supercells with the linear sum of the pure Sn/Ti absorption spectra, shown in Figure , where almost identical spectra are obtained apart from some small differences due to weak halide band broadening in the mixed-cation supercells. We note here that explicit GW+BSE calculations for the 72-atom mixed-cation supercells used in this work are far from computationally tractable, with such calculations already at the limit of current computational capacity with the 9-atom unit cells of the pure-phase materials.