Unoccupied surface states on clean and oxygen-covered Cu(110) and Cu(111)

The experimentally observed surface states of the adsorbate systems Cu(110)p(2×{}1)O and Cu(111)/O₂ can be simulated by a simple model using a planar-averaged surface barrier. The E(k?) dispersion curves of the adsorbate case are obtained from those of the clean-surface case by a systematic downward shift in energy which is achieved, in this particular model, by an outward movement of the barrier by 1--2 a.u.