Connection between charge transfer and alloying core-level shifts based ondensity-functional calculations

The measurement of alloying core-level binding energy (CLBE) shifts has bee n used to give a precise meaning to the fundamental concept of charge trans fer.:Here, ab initio density-functional calculations for the intermetallic compound MgAu are used to investigate models which try to make a connection between the core levels shifts and charge transfer. The calculated CLBE sh ifts agree well with experiment, and permit an unambiguous separation into initial-state and screening contributions. Interestingly, the screening con tribution is large and cannot be neglected in any reasonable description. C omparison of the calculated results with the predictions of simple models s how that these models are not adequate to describe the realistic situation. On the positive side, the accuracy of the density-functional calculations indicates that the combination of experiments with such calculations is a p owerful tool to investigate unknown systems.