Tight-binding coherent-potential-approximation study of the electronic states of palladium–noble-metal alloys

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Abstract
We have performed calculations of the electronic states of palladium–noble-metal disordered alloys using an improved version of the tight-binding coherent-potential-approximation (TB-CPA) formalism. Our results for Pd-Ag are in excellent agreement with both experiment and the Korringa-Kohn-Rostoker (KKR) CPA. For Pd-Au we also obtain good agreement with specific-heat measurements. For Pd-Cu, probably due to charge-transfer effects, we do not obtain satisfactory agreement with experiment at the Cu-rich end. Our calculations indicate that if (a) highly accurate Slater-Koster parameters are used and (b) all the orbitals are included in the CPA conditions (i.e., not using a one-level TB model), the TB-CPA gives results that are equivalent to those of the KRR-CPA except in cases where off-diagonal disorder might be important.