Initially, it is evident that the core features of the band structure, such as the dispersion along Γ to X and the correspondent localisation of states along Γ to Z are replicated in both quasiparticle methods here, as well as the HSE06 band structure. A minor change from HSE06 is the increased splitting of the degenerate Ti d conduction bands along Γ to N. More significantly, the quasiparticle gap is significantly greater -3.05 eV with QSGW compared to the fundamental HSE06 gap of 1.95 eV. QSGW is expected to systematically overestimate band gaps due to the omission of the vertex and incomplete screening effects within the RPA, typically only by 10% in s/p semiconductors, but the effect can be much larger in Mott-Hubbard insulators such as NiO. The addition of ladder diagrams, and thus additional screening due to the electron-hole interactions, to the screened Coulomb W in the QSG Ŵ method is expected to account for the majority of the latter effect -in Y 2 Ti 2 O 5 S 2 , it does reduce the gap, but only by 60 meV to 2.99 eV. This difference in band gap, of over 1 eV between the hybrid DFT and quasiparticle band structures, is considerable, though is similar to that seen in the caesium titanium halides, which similarly have an anionic-dominated valence band and Ti d conduction band. difference will be revisited when considering the optical spectrum.