Charge transfer in alloys: AgAu

The relationship of charge transfer in alloys to electronegativity, to relative pure-constituent Fermi energies, and to atomic volume is discussed. The importance of using comparable potentials for alloy calculations is emphasized. The results are illustrated by coherent-potential-approximation calculations for AgAu alloys using an $s\ensuremath{-}d$ model Hamiltonian. Charge transfer as a function of concentration and the assumed pure-metal Fermi-energy difference has been calculated self-consistently including the shift of the $d$-band energies resulting from the modified electron-electron Coulomb interaction. Renormalized-atom estimates are used for the Coulomb integrals which relate the shift in one-electron energies to the charge transfer. The result is in reasonable agreement with the charge transfer inferred from isomer-shift and x-ray-photoelectron-spectroscopy core-level-shift measurements. Using the proper charge transfer, the calculated optical-absorption edge agrees with ${\ensuremath{\epsilon}}_{2}$ experiments, and the self-consistently determined Fermi energy has the same qualitative concentration dependence as measured work-function differences for the alloy system.