Corrugation studies forp(2×2) and c(2×2)phases of oxygen on Ni(001) and Cu(001)

Chemisorption of oxygen on Ni(001) shows $p(2\mathrm{}\times 2)$ low-energy electron diffraction (LEED) patterns at low exposures changing to $c(2\mathrm{}\times 2)$ at higher exposures. A recent quantum-mechanical cluster calculation and a lattice-dynamical calculation have suggested different vertical heights for the two phases of oxygen. Another ab initio cluster calculation and extended x-ray-absorption fine-structure data indicate a single vertical height, in agreement with earlier LEED studies. More recent LEED calculations, however, do not rule out a closer distance for the $c(2\mathrm{}\times 2)$ phase. A He-diffraction study has just been completed for the $c(2\mathrm{}\times 2) \mathrm{and} p(2\mathrm{}\times 2)$ phases. We compare our calculated corrugation with these data and conclude that in both phases oxygen is at a vertical distance of about 0.9 Å. We predict similar results for oxygen on Cu(001).