Likewise, in the independent-particle absorption spectra of the mixed compounds calculated using hybrid DFT with spin-orbit coupling (HSE06+SOC)(Figure ,fError! Reference source not found.), we find minimal peak shifting or mixing, with the total absorption essentially being a linear combination of the tin and titanium related absorption features, weighted by the mixing fraction x. These calculations reveal that Ti-rich compounds have much stronger absorption intensity than the Sn-rich vacancy-ordered perovskites -due to reduced band dispersion and increased number of electronic states for Ti d vs Sn s (i.e. 10 vs 2) which contributes to the dominance of the TiX 6 excitonic peaks in the absorption spectra of the mixed compounds even at very low percentage concentrations of Ti. While these single-particle spectra individually are not quantitatively reliable due to the presence of strong excitonic effects as shown in our previous work, they allow us to qualitatively assess the impact of cation mixing on the quasi-particle electronic structure -here demonstrating additive behavior and minimal hybridization. The lack of cation orbital mixing or hybridization is further exemplified by the electronic densities of states (DOS) and band structure plots in Figures , which show negligible hybridization of the Ti d and Sn s states, with only their relative intensity varying as a function of the Sn fraction x. If we take these insights and plot the linear sum of the pure-phase excitonic absorption spectra, previously calculated using GW+BSE@HSE06+SOC, we in fact find a good match with the experimentally-measured and (e) show the expected absorption spectra from taking a linear combination of the pure phase spectra computed using GW+BSE (including excitonic effects) reported in Kavanagh et al.,