MgO addimer diffusion on MgO(100):: A comparison of ab initio and empirical models -: art. no. 115437

Diffusion of a MgO dimer on a MgO(100) surface is investigated using both density functional theory (DFT) and empirical ionic potentials. Barriers for diffusion via hop and exchange mechanisms are calculated. A qualitative difference is found between DFT and the empirical potential for the oxide exchange barrier. DFT predicts a saddle point for the process with a barrier of 0.88 eV, whereas the empirical potential of Lewis and Catlow, with a formal charge of +/- 2.0e, finds this structure to be a stable intermediate minimum with an energy of 0.19 eV, relative to the most stable addimer structure. The empirical potential predicts that the oxide hop and exchange mechanisms are equally likely; whereas, DFT shows that the oxide adion hop mechanism has a lower energy barrier. A Bader population analysis of the DFT charge density indicates that the magnesium and oxide ions have partial charges of magnitude +/- 1.7e. Using an empirical potential with this partial charge, the local minimum in the oxygen exchange process becomes a saddle at 0.62 eV, which is in better agreement with DFT. The standard deviation between the energy of the DFT minima and the saddle points with those of the empirical potential was reduced from 0.32 eV when using the formal charge parameters of Lewis and Catlow to 0.15 eV using partial charges. The qualitative agreement found for each diffusion barrier using the partial charge model suggests that a Bader analysis can be used to obtain suitable partial charges for constructing empirical potentials.