QUANTUM-WELL STATES IN CU CO OVERLAYERS AND SANDWICHES/

We report ab initio calculations of quantum-well states in Cu/Co(001) and Co/Cu(001) overlayers and in Co/Cu/Co(001) sandwiches. Overlayer s tates are found which coincide well with those previously identified i n photoemission and inverse photoemission experiments. In Cu/Co and at energies overlapping with the substrate continuum, minority spin reso nances are clearly identifiable. However, in the majority spin channel coupling to the substrate is strong enough to effectively destroy qua ntum-well features. In Co/Cu/Co(001) sandwiches discrete states are fo und at similar energies to those in overlayers of corresponding Cu thi cknesses, but well defined resonance states are absent in both spin ch annels. There is no longer a strongly size-dependent electronic struct ure at the Fermi energy We conclude care must be taken in extrapolatin g from the electronic structure of overlayer systems to that of other modulated structures.