Adsorption of CO at various sites on Ni(7 5 5) has been investigated by density functional theory method (periodic DMol(3). The bridge site parallel to the (1 0 0) step is most favorable and the atop site on the (1 1 1) terrace is least stable, although the difference of adsorption energy is 0.37 eV. The other sites on the terrace and step are intermediate. There is only small binding energy preference for step sites, which can explain the similarity of temperature-programmed desorption spectra for CO on Ni(7 5 5) to those for Ni(1 1 1). (C) 2003 Elsevier Science B.V. All rights reserved.