Cation adatom diffusion on the NiO(0 0 1) surface by molecular dynamics simulation

We present results concerning the diffusion of Ni2+ adatom on the (0 0 1) surface of NiO obtained by molecular dynamics simulations based on a rigid ion potential model. A wide temperature region was covered ranging from 0.29Tm up to 0.85Tm, Tm being the melting point of the model system. Two possible adatom positions were found on the surface in accordance with static calculations. From the detailed analysis of the ionic trajectories it came out that the adatom diffuses on the surface via hopping and exchange mechanisms. Both processes exhibit Arrhenius behavior from where we deduced the corresponding migration energies. In addition, we found two distinct temperature regions reflecting different energetic requirements for hopping diffusion. This is due to the spontaneous creation of anionic adatom that combine with the cationic adatom at high temperatures. Moreover, we found that although the frequency rates for hopping and exchange are comparable, the exchange mechanisms participate to the diffusion coefficient more than the hopping process by as much as an order of magnitude at high temperatures.