The lattice parameters of the conventional unit cell, optimised using both PBEsol and HSE06, are listed and compared to experimental measurements and other calculations in Table . The calculated lattice parameters closely agree with measurements, with the volume of the relaxed unit cell decreasing by only 1.3% (PBEsol) and 0.4% (HSE06) relative to the experimental structure. The structural relaxations with both functionals generally shortened the Y-O and Y-S bonds in the YO 4 S 5 motif (Figure ), with the exception that the axial Y-S bond was elongated by 0.02 A in the HSE06 optimisation. The equatorial Ti-O bonds in the TiO 5 S octahedra (Figure ) were shrunk by 0.006 A, while the axial relaxation differed between the two functionals such that in the PBEsol-relaxed structure the axial Ti-O and Ti-S bond lengths increased and decreased, respectively, whereas the opposite was observed in the HSE06-relaxed structure. The greater volume contraction in the PBEsol-relaxed structure can be predominantly attributed to the axial Ti-S and Y-S bonds shortening by 0.021 A and 0.048 A, respectively, whereas the lengths of these two bonds were increased by 0.022 A and 0.017 A in the HSE06 structure.