To examine the convergence of the PBE+D3 adsorption energy with the cluster size, we compared adsorption energies calculated for two progressively larger clusters with the result from periodic DFT calcualtions. This step is crucial for assessing the validity of the cluster models used to approximate the periodic system. Results are reported in Table . At the PBE+D3 equilibrium structure of Co/Mg(O), as the cluster size increases from Co/Mg 9 O 9 to Co/Mg 25 O 25 , the long-range correction, ∆ LR = ∆E ads (pbc) -∆E ads (cluster),