Auger Energy Shifts for Metallic Elements

A previous treatment of core-level binding-energy shifts for metals is extended to Auger energy shifts. In comparison to single core-hole shifts, the new information given by the Auger shift is contained in the shift of the two core-hole final state. An accurate expression for the shift of the two core-hole ionization energy between the free atom and the metal is derived. In the actual calculation of the shift a ( Z + 2) equivalent core approximation is applied, but where important corrections are included. Comparison between theory and experiment is performed for the metallic elements Na-Al, Ni-Ga, Pd-Sn, Au, Tl-Bi, Ba and Yb, and in all cases a good agreement is obtained. A rather detailed compilation of atomic and solid phase double-hole energies is presented in the Appendices. To elucidate the break-down of the concept of metallic screening, non-conducting elements like Si, Ge-Se, Sb and Te are also considered. In addition, atom-metal two core-hole energy shifts are calculated for the 4 d transition series and an abrupt change in the energy shift is found when we proceed from the d elements to the elements beyond. The influence of the atomic structure on the shift is considered for the 4 d n 5 s 2 , 4 d n +15 s and 4 d n +2 configurations. The metallic renormalization of the atomic core-hole Coulomb correlation energy is calculated for the 4 d elements and the chemical shift of this quantity is shown to be closely related to the change of the Auger parameter. The present formalism provides a most suitable framework for treating chemical shifts in metallic systems. As a special example the situation at the surface of a metal is considered and surface shifts are predicted both for the two-hole and the Auger energies. As for the single core-holes, these surface shifts change sign as we proceed through a transition series due to the bonding-antibonding division of the d -band.