A remaining question is then the suitability of hybrid DFT as a predictive tool, given that Y 2 Ti 2 O 5 S 2 is predicted to be highly excitonic within many-body perturbation theory. In Figure , the absorption coefficients calculated using the three theoretical methods are compared within the relevant spectral region (up to the near-mid UV), and it is evident, that despite the absence of many-body effects within DFT, the HSE06 optical absorption matches very well to that of QSG Ŵ +BSE in both the slow initial onset followed and the strengthening above 3 eV, with the exception of the excitonically-enhanced peak in the latter above the quasiparticle gap. While this agreement may be fortuitous -though it may be noted that the functional form of HSE06 includes the effect of screening on the exchange interaction -it demonstrates that HSE06 can be reliable at generally predicting the optical behaviour and onset of Y 2 Ti 2 O 5 S 2 , and thus that the trends established using hybrid DFT are valid in comparison with higher-level theoretical methods.