2.4 eV ), indicating that once OH * is generated, it is thermodynamically favourable for it to desorb as solvated hydroxyl radical rather than recombine at the surface to produce a metal hydroxide group. This suggests a strong tendency for CaTiO 3 to generate hydroxyl radicals, aligning with experimental findings from UV-illuminated CaTiO 3 , which demonstrate the production of hydroxyl radicals with the energy of holes during UV exposure estimated at around 2.5 V . Furthermore, the free energy of H 2 O 2 is significantly higher than that of O * , indicating that metal-oxo complex (O * ) could serve as a potential secondary oxidation product.