Density functional study of the interaction of molecular oxygen with small neutral and charged silver clusters

O2 adsorption on small neutral, anionic and cationic silver clusters Agn (n = 1-7) has been studied by using the PW91PW91 density functional method. The adsorption energies of O2 on the anionic and neutral clusters have an odd-even alternation pattern clearly, and our calculations give the same adsorption behavior of O2 on silver cluster anions as the experimental measurements. The adsorption energies on the cationic clusters, instead, are generally smaller than those on the anionic and neutral clusters, and reach a local maximum at Ag4O2+. Natural bond orbital analyses show that electrons mostly transfer from silver atoms to molecular O2 except for the smallest silver cluster cations (n = 1-3).