Work-function anisotropy in noble metals:: Contributions from d states and effects of the surface atomic structure

The work functions of high-density Cu and Au surfaces are studied by ab initio calculations. We determine the work-function dependence on the crystallographic orientation of the surface and extract the separate contributions from the s and d states. The face-dependent contributions to the surface dipoles from the d states are shown to follow a trend different from that of the s states, which is predicted by Smoluchowski's smoothing argument. The influences on the work function of surface relaxations in Cu and of surface reconstruction for Au(110) are also considered. These effects are explained in terms of surface effective charges at relaxed surfaces and by a microscopic model of the charge rearrangement at the reconstructed surface.