Chemisorption Bonding ofc(2×2)Chalcogen Overlayers on Ni(001)

Calculated low-energy electron diffraction spectra for $c(2\mathrm{}\times 2)$ overlayer structures of O, S, Se, and Te on Ni(001) show very good agreement with experiment for fourfold coordinated bonding sites and displacements of 0.90, 1.30, 1.45, and 1.90 ± 0.1 Å, respectively, from the center of the first layer of nickel atoms. These adsorbate-atom locations correspond to Ni-chalcogen bond lengths smaller than occur in bulk compounds, but comparable to those found in divalent Ni-chelate complexes.