Grand Canonical Monte Carlo simulations were used to study the growth of a Na layer onto a O-p(2 x 2)-Pt(1 1 1) surface At the beginning of the deposition the film presents a disordered structure which becomes progressively ordered as the coverage increases due to the repulsive lateral interactions between the adsorbates We found some ordered structures like p(16 x 16) p(14 x 14) and p(12 x 12) which appears at coverages I lower than Theta similar to 0 007 in all these overlayers the Na adatoms are adsorbed on fcc-hollow sites of the oxide surface (C) 2010 Elsevier Ltd All rights reserved