In the recent decade in particular, there has been intensive focus in the detailed modelling of surface reaction for catalysis, of which TiO2 and now CeO2 are the prototypical examples. Highthroughput electronic-structure calculations have provided us with atomistic insights on the fundamental issues of reactive surface chemistry, e.g., (I) understanding the intrinsic mechanism of defect formation; (II) understanding the dynamics of defects and localized polarons during metastable and at equilibrium state; (III) understanding how these surface defects can influence the structure-activity relationship with the reactive species for a given chemical reaction.