The adsorption of cyclopentene (c-C5H8) on Ni(111) was studied using DFT and semiempirical calculations. Preferred site and geometry calculations were carried out considering a Ni(111) surface and a unit cell of 64-atoms. The tetrahedral threefold hollow position was identified as the most favorable site, with a surface-molecule minimum distance of 1.83 angstrom. A bending structure is adopted when the molecule is adsorbed where the carbon atoms of the double bond are closer to the surface forming an angle of 160 among non-equivalents carbon atoms. The metal surface was represented by a two-dimensional slab with an overlayer of c-C5H8/Ni of 1/9 ratio. We also computed the density of states (DOS) and the Crystal orbital overlap populations (COOP) Corresponding to C-C, C-Ni, C-H, and Ni-Ni bonds. We found that both Ni-Ni bonds interacting with the ring, and the C=C bond are weakened after adsorption, this last bond is linked significantly to the surface. The hydrogen atoms belonging to the saturated carbon atoms also participate in the adsorbate-surface bonding. The main interactions include the 4s, 3p, and 5d(z2) bands of nickel and 2(pz) bands of the carbon atoms of the double bond. (C) 2008 Elsevier B.V. All rights reserved.