Electronic structure of noble-metal monoxides: PdO, PtO, and AgO

The electronic structure and properties of the noble-metal monoxides, PdO, PtO, and AgO have been determined by the full-potential linearized augmented-plane-wave (FLAPW) and full-potential linear-muffin-tin-orbital (FLMTO) methods. The calculated band structures show PdO and PtO to be poor metals with very low densities of states at the Fermi level. Thus, as in the 3d oxides, both methods used within the scope of the local-density approximation fail to produce the band gaps observed experimentally for PdO and PtO; they do, however, show that these band gaps are of the type that occur from crystal-field effects rather than being of the Mott-Hubbard or charge-transfer type. For AgO, the monoclinic crystal-field splitting of the d states is strong enough to induce a small direct band gap, which partially separates the electronic states of two nonequivalent silver atoms and results in Ag1+ and Ag2+ configurations rather than Ag1+ and Ag3+. Thus, correlation effects appear to be important for the detailed description of electronic states near EF not only for 3d metal monoxides, but for noble-metal oxides with much-less-localized metallic d states. Finally, the excellent agreement between the FLAPW and FLMTO results shows the possible advantage of using the much-less time-consuming FLMTO method in quantitative band-structure calculations of complex crystals.