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

Chemisorption of oxygen on Ni(001) shows p (2×2) low-energy electron diffraction (LEED) patterns at low exposures changing to c (2×2) 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 (2×2) phase. A He-diffraction study has just been completed for the c (2×2) and p (2×2) 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. We predict similar results for oxygen on Cu(001). © 1983 The American Physical Society.