Electronic Structure of Ultrathin Transition and Noble Metal Films with Simple Metal Interfaces

We have developed a technique within the framework of the Green's function method for calculating the changes in electronic structure of d-band metals associated with going from a bulk to an ultrathin (oligatomic) film geometry. The formal result making high quality calculations of this type practical is that the film problem with a vanishing wavefunction boundary condition has electronic eigenfunctions which, within the film boundaries, are identical to those of an appropriately defined three-dimensional periodic tetragonal complex lattice. The boundary where the wave functions are constrained to vanish can lie outside the physical boundary limiting the region where the potential corresponds to the d-band metal, and can vary with energy. This has enabled us to allow for electron leakage from the d-band metal film and accurately simulate either the situation of a d-band metal film suspended in vacuum, or the more experimentally realizable situation of an ultrathin film of a d-band metal with interfaces with a simple metal. We show results for the latter situation for a monlayer of copper. These calculations predict striking changes from bulk behavior in agreement with photoemission experiments.