Reduction of O-2 in the presence of model PtVFe nanocatalysts was studied using the PBE functional with a plane wave basis set. The model catalysts consisted of trimers and a 0.6-nm particle. The results show that among three molecular chemisorption configurations, i.e. Pauling, Griffith, and Yeager configurations, the O-2 bond is weakened the most in the Yeager configuration, then the Griffth configuration, and then the Pauling configuration. A new molecular chemisorption configuration, i.e. 5-atom ring configuration, was also identified. With the O-O distance up to 1.4 angstrom, a linear correlation was found between the O-2 stretching frequency and the O-2 bond distance regardless of the metal or adsorption site. However, the charge transfer and the adsorption energy are highly dependent on the metal and adsorption site. The alloyed clusters are most effective in transferring electrons to O-2 species and weakening O-2 bond especially when the O atoms are attached to non-Pt atoms. Our results suggest that the superior catalytic activity of PtVFe nanoparticles in the oxygen reduction is due to the effectiveness in charge transfer and the presence of direct (spontaneous) dissociation pathway. (c) 2011 Elsevier B.V. All rights reserved.