CHARGE REDISTRIBUTION AT PD SURFACES - AB-INITIO GROUNDS FOR TIGHT-BINDING INTERATOMIC POTENTIALS

A simplified tight-binding description of the electronic structure is often necessary for complex studies of surfaces of transition-metal co mpounds. This requires a self-consistent parametrization of the charge redistribution, which is not obvious for late transition series eleme nts (such as Pd, Cu, Au), for which not only d but also s-p electrons have to be taken into account. We show here, with the help of ab initi o full potential Linear muffin-tin orbital approach, that for these el ements the electronic charge is unchanged from bulk to the surface, no t only per site but also per orbital. This implies different level shi fts for each orbital in order to achieve this orbital neutrality rule. Our results invalidate any neutrality rule which would allow charge r edistribution between orbitals to ensure a common rigid shift for all of them. Moreover, in the case of Pd, the power law which governs the variation of band energy with respect to coordination number, is found to differ significantly from the usual tight-binding square root.