Electron-hole interactions are found to dramatically redshift (Tables and and Fig. ) and qualitatively alter the absorption spectra for Cs 2 TiX 6 , now yielding excellent agreement with the peaked experimental spectra. Analysis of the electronic states reveals the lowest energy bright exciton peak to originate from the t 1u (π + σ) → t 2g (d) electronic transition as expected, i.e. from the second-highest valence band (ψ VBM-1 ) at Γ (Fig. ) to the CBM. The lowest energy dark excitonic state, indicated by the arrows in Fig. and located 0.3-0.4 eV below the first bright peak, corresponds to the symmetry-forbidden t 1g (π) ψ VBM → t 2g (d) ψ CBM transition mentioned previously. While improved agreement with the experimental spectra is found for all Cs 2 TiX 6 isomorphs, smaller changes in the spectral shapes are noticed for X = Br, Cl. This results from the low band dispersion in these compounds (demonstrated by the large effective masses in Table ), resulting in similar strong excitonic downshifting of the low-energy excitations; t 1u (π + σ) → t 2g (d) and t 2u (π) → t 2g (d) corresponding to ⟨ψ VBM-1 |H ′ |ψ CBM ⟩ and ⟨ψ VBM-2 |H ′ |ψ CBM ⟩ transitions. Indeed in their recent paper, Grandhi et al. refer to the absorption onset of Cs 2 TiBr 6 as an exciton peak, with our calculations revealing in fact both low-energy peaks to be excitonic in nature. This strong renormalization of the low-energy excitations and lack of a band-like absorption onset rules out standard spectrum fitting techniques (such as the Tauc and Elliott models) for extracting band gap and exciton binding energies. Notably, the experimental spectra for TiBr 2and TiCl 6 2salts reported in Brisdon et al. closely resemble the results for Cs 2 TiBr 6 and Cs 2 TiCl 6 reported here and in the literature, evidencing the conclusion of molecular crystal behavior, the orbital assignments of the absorption peaks and the presence of strong electron-hole interactions. Improved agreement between the calculated and experimental spectra is also found for the Sn compounds upon inclusion of electron-hole interactions, as weaker exciton interactions modify transition intensities and shift spectral weights to give more peak-like absorption onsets. The small residual mismatch in some cases between the GW +BSE and experimental spectra could be a result of temperature effects (vibrations can lower the symmetry-restriction of dark excitonic transitions in this range), quasiparticle lifetime broadening or the neglect of higher order terms in GW . We highlight that the low-energy absorption peaks for Cs This form of exciton is commonly witnessed in organic and molecular crystals, and has been well-established in other 3d 0 (Ti 4+ , Sc 3+ , Ca 2+ ) halides, arising here as a consequence