Ab initio explanation of tunneling line shapes for the kondo impurity state.

We report an ab initio study of the Kondo states formed from a Co adatom on Cu(111) and Cu(100). The model consists of a CoCun cluster ( n = 5-19) embedded in (111) and (100) Cu slabs. An embedding potential derived from density functional theory treats the interaction between the periodic crystal surroundings and the CoCun cluster, while strong electron correlations within CoCun are explicitly accounted for via configuration interaction (CI) methods. Analysis of the embedded CI wave function provides insight into the nature of the Kondo state, specifically into the influence of the crystal host on the Co d-electronic structure. We predict that different d-orbitals are preferentially singly occupied in Co on Cu(111) versus Cu(100) as a result of the different crystalline environment. We propose that these variations in the local d-electronic structure on Co, not accounted for in previous theories, are responsible for the drastically different Kondo resonance line shapes observed in scanning tunneling microscopy experiments on these two surfaces.