CORE-LEVEL SHIFTS AT BCC TRANSITION-METAL SURFACES DEDUCED FROM THE CALCULATION OF SURFACE SEGREGATION ENERGIES

Within the equivalent core approximation, the core level shift between surface and bulk atoms is equal to the surface segregation energy of an impurity of atomic number Z + 1 in a matrix of atomic number Z. The se energies have never been calculated systematically but have been de duced from thermodynamical data using additional approximations. We pr esent here a tight-binding study of these segregation energies and com pare them with previous approaches to the calculation of surface core level shifts. The agreement between theory and experiments is signific antly improved.