We report a detailed density functional theory (DFT) study of the geometrical and electronic properties, and the growth mechanism of a Cu_{n} (n = 1–4) cluster on a stoichiometric, and especially on a defective CeO_{2} (110) surface with one surface oxygen vacancy, without using pre-assumed gas-phase Cun cluster shapes. This gives new and valuable theoretical insight into experimental work regarding debatable active sites of promising CuO_{x}/Ceo_{2} - nanorod catalysts in many reactions. We demonstrate that CeO_{2}(110) is highly reducible upon Cun adsorption, with electron transfer from Cu_{n} clusters, and that a Cu_{n} cluster grows along the long bridge sites until Cu_{3}, so that each Cu atom can interact strongly with surface oxygen ions at these sites, forming stable structures on both stoichiometric and defective CeO_{2}(110) surface. Cu–Cu interactions are, however, limited, since Cu atoms are distant from each other, inhibiting the formation of Cu–Cu bonds. This monolayer then begins to grow into a bilayer as seen in the Cu_{3} to Cu_{4} transition, with long-bridge site Cu as anchoring sites. Our calculations on Cu_{4} adsorption reveal a Cu bilayer rich in Cu^{+} species at the Cu–O interface
