Context <p>The study presents a comprehensive computational analysis of CO adsorption on anatase TiO₂ surfaces with the (001) and (111) facets, utilizing CO as an IR probe. CO adsorption orientations and binding strengths vary between surfaces due to differences in local surface geometries and Ti coordination environments. Detailed electronic structure analyses, including density of states and wavefunction visualizations, show that σ-donation dominates on the (111) [TiO₃] site. At the same time, π-backdonation is more prominent at the (111) [TiO₅] site, correlating with a blue shift of the CO stretching frequency for the (111) [TiO₃] site and a red shift for the (111) [TiO₅] site. Surface oxygen atoms are key contributors to π-backdonation. The results highlight the critical role of surface topography and coordination environment in governing CO adsorption behavior, extending previous insights into anatase surface chemistry.</p> Methods <p>All periodic calculations were performed using the Vienna ab initio package (VASP), employing the GGA-PBE functional and a plane-wave basis set, with the projector-augmented wave (PAW) method for the description of core electrons. All cluster calculations were performed using the ORCA package. We employed the PBE and B3LYP functionals, as well as the MP2 wavefunction–based method, all with the TZVP basis set. For the localized average ionization energy (ALIE), we employed the CCSD(T)/aug-cc-pV5Z level of theory.</p>