Surface structure and core-level shifts in lead chalcogenide (001) surfaces

We study the geometrical structure, the relaxation, and the surface core-level shifts of PbS and PbTe (001) surfaces via ab initio pseudopotential. calculations. In both systems, an oscillatory relaxation of the surface-layer separations is predicted and this feature is expected to be present in other polarizable ionic rocksalt compounds. In agreement with experiment, PbTe displays a large surface rumpling that is absent in PbS. Reasons far these similarities and differences are addressed. Our results compare well with most available experimental data. Partial disagreement with a recent x-ray standing wave investigation in PbS is discussed. Core-level shifts in PbS are very small and ate not sensitive to surface relaxation. Therefore, they are not a useful tool to investigate surface geometry in these compounds.