- We have studied theoretically the differences in metallic film growth modes between perfect and defective oxide substrates by combining ab initio hybrid B3LYP periodic calculations on the corresponding 2D slab models of Me/MgO(0 0 1) interfaces (Me = Ag, Cu) with thermodynamic theory of solid solutions. We observed a strong change of the bonding between the metal adatoms and substrate in the vicinity of the surface Fs centers (neutral O vacancies), which affects the thermodynamic conditions and the morphology of the growing metallic layer. For a perfect magnesia surface, we confirm the experimentally observed sub-monolayer growth of metallic islands (Ag possesses a higher trend toward such adatom aggregation than Cu). The surface Fs centers weaken the trend toward metal atom aggregation and above some critical concentration lead to formation of disordered 2D metallic films; i.e. the island formation mode is replaced by the layer-by-layer growth mode.