Diffusion of adatoms and small clusters on magnesium oxide surfaces

The diffusion of isolated adatoms and small clusters is reviewed for transition and noble metals adsorbed on the (001) surface of magnesium oxide. While isolated adatoms diffuse by hopping among adsorption sites, small clusters such as dimers, trimers and tetramers already display a variety of diffusion mechanisms, from cluster hopping to rotation, sliding, leapfrog, walking, concertina, flipping, twisting, rolling and rocking. Since most of the available results are computational, the review is mostly related to theoretical work. Connection to experiments is discussed where possible, mostly by dealing with the consequences that adatom and small cluster mobility may have on the growth of larger aggregates on the MgO(001) surface.