Charge transfer in transition-metal alloying: Charge-tailing effects

Charge transfer in alloys is normally discussed in terms of band hybridization, band filling, and screening, but at times experiment and theory yield apparently odd results where, for example, rare-earth actinides or elements from the Ti column apparently gain charge from electronegative transition metals such as Fe, Pt, or Au. Here it is observed that there are charge-tailing terms, due to tails of charge associated with an atom's nearest neighbors, which make substantial contributions to the change in charge count at a site in a compound. This is shown with linearized augmented Slater-type-orbital calculations for 5d transition-metal alloys in the ordered CsCl structure. That charge transfer that remains, after the tailing effects are subtracted out, is seen to be consistent with notions concerning electronegativity behavior (though indicating Pt rather than Au to be the most electronegative of the 5d elements). These findings have serious implications for understanding charge transfer and make it necessary to reexamine almost all the arguments relating charge transfer to the bonding of transition metals and, for that matter, of main group elements.