Large lattice-relaxation-induced electronic level shifts in randomCu1−xPdxalloys

Mean-field theories of unrelaxed ${\mathrm{Cu}}_{0.75}$ ${\mathrm{Pd}}_{0.25}$ alloys exhibit a deep (${\mathrm{\varepsilon }}_{\mathit{F}}$-5.5 eV) Pd bonding state at the bottom of the Cu d band that does not show up in photoemission experiments. We have applied the ‘‘special quasirandom structures’’ construct to ${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pd}}_{\mathit{x}}$ alloys in the context of local-density total-energy minimization, finding a distribution of Cu-Cu, Cu-Pd, and Pd-Pd bonds whose lengths deviate significantly from the single, unrelaxed value assumed in mean-field models. Such lattice distortions are found to induce a ∼1-eV shift in the Pd bonding state to lower binding energies, thus removing much of the discrepancy with experiment.