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(2x1)O and Cu(111)/O sub 2 can be simulated by a simple model using a planar averaged surface barrier. The E(k sub 11) 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.