• DFT calculations of adsorption and diffusion of O, O 2 , OH and H 2 O on Cu(100) surfaces were performed. • H 2 O prefers to bind weakly on a top site through the oxygen atom. • O, O 2 and OH adsorb on a hollow site. • Diffusion velocity values were obtained for all species. • Water diffuses faster over the Cu(100) surface and O2 does it more slowly. [Display omitted] An extensive study of adsorption and diffusion of O , O 2 , O H and H 2 O on C u (100) surfaces was performed by means of DFT calculations. The adsorption distances and energies of the different species on top, hollow and bridge sites of the C u (100) surface were calculated in order to elucidate preferential adsorption sites. All these calculations were done in conjunction with a study of charge distribution. The O , O 2 and O H species, were found to adsorb preferentially on hollow , while H 2 O was found to adsorb on top , through the oxygen atom. Also, diffusion of each species from the most stable adsorption site to the nearest neighbouring site was studied in order to obtain diffusion barriers and diffusion velocity values. The diffusion of H 2 O and O H was found to be faster than the other species, whereas the O 2 molecule was the lowest. [ABSTRACT FROM AUTHOR]