in this study, we determine the effects of having vacancies on the Pt(111) surface to the dissociative adsorption behavior of H(2) on Pt(111). We study the potential energy behaviors along the reaction paths based on the potential energy surfaces (PESs) we calculated that are relevant to these systems. Partial results of our current calculations, based on the density functional theory, reveal that vacancies on the substrate can significantly lower the barrier for the dissociative adsorption of H(2) on the Pt(111) surface. We attribute this behavior to the increased reactivity of the surface owing to the vacant sites. Of the substrate atoms, we find that those on the surface mainly influence the behavior of H(2) adsorption on Pt(1 11). Copyright (C) 2008 John Wiley & Sons, Ltd.