  The measurement of alloying core-level binding energy (CLBE) shifts has been used to give a precise meaning to the fundamental concept of charge transfer. 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 shifts agree well with experiment, and permit an unambiguous separation into initial-state and screening contributions. Interestingly, the screening contribution is large and cannot be neglected in any reasonable description. Comparison of the calculated results with the predictions of simple models show 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 powerful tool to investigate unknown systems. 
Connection between charge transfer and alloying core-level shifts based   on density-functional calculations