THE ADSORPTION OF BENZENE ON NI(111)

Using a many-electron embedding theory, the present work treats the adsorption of benzene on Ni(111) by modelling the lattice as a 28-atom, three-layer cluster. Ab initio valence orbital CI calculations carried out on a local surface region permit an accurate description of bonding at the surface. Benzene is found to be adsorbed molecularly, parallel to the surface, at a threefold site, bonding primarily through its pi-electron system. The equilibrium distance is 2.2 angstrom from the surface. The calculations show no distortion of the benzene ring, other than a 2% expansion. C-H bonds tilt away from the surface 8.5-degrees. The adsorption energy is calculated to be 1.2 eV. Adsorption at the threefold hollow site gives a slightly higher energy than the hcp site, but the difference may be within the uncertainty of the calculation. The energy of the bridge adsorption site is higher than that of the hcp site, by 0.8 eV. Atop atom sites were not investigated. Due to the limited number of geometries investigated. particularly those involving Kekule and buckling distortions, some aspects of the benzene geometry and energetics of different sites remain uncertain.