POTENTIAL, CORE-LEVEL, AND D-BAND SHIFTS AT TRANSITION-METAL SURFACES

We have extended the validity of the correlation between the surface 3 d core-level shift (SCLS) and the surface d band shift (SDBS) to the e ntire 4d transition-metal series and to the neighboring elements Sr an d Ag via accurate first-principles calculations. We find that the corr elation is quasilinear and robust with respect to the differencies bot h between initial- and final-state calculations of the SCLS's and two distinct measures of the SDBS's. We show that despite the complex spat ial dependence of the surface-potential shift (SPS) and the location o f the 3d and 4d orbitals in different regions of space, the correlatio n exists because the sampling of the SPS by the 3d and 4d orbitals rem ains similar. We show further that the sign change of the SCLS's acros s the transition series does indeed arise from the d band-narrowing me chanism previously proposed, However, while in the heavier transition metals the predicted increase of d electrons in the surface layer rela tive to the bulk arises primarily from transfers from s and p states t o d states within the surface layer, in the lighter transition metals the predicted decrease of surface d electrons arises primarily from fl ow out into the vacuum.