Mixed excitonic nature in water-oxidized <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>BiVO</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:math> surfaces with defects

${\mathrm{BiVO}}_{4}$ is a promising photocatalyst for efficient water oxidation, with surface reactivity determined by the structure of active catalytic sites. Surface oxidation in presence oxygen vacancies induces electron localization, suggesting an atomistic route to improve charge transfer efficiency within cycle. In this paper, we study effect on electronic and optical properties at surfaces upon oxidation. We use density functional theory many-body perturbation explore change quasiparticle energy levels evaluate electron-hole coupling as function underlying structure. show that while defects alters atomic largely modifies wave-function nature, leading defect-localized states gap region, excitations remain unchanged due substantial hybridization defect nondefect transitions. Our findings suggest defect-induced supports improved transport, both through bound tunable via mixed nature transitions, expected reduce trapping.