Impurities and defects in transition metals and their oxides

Self‐consistent local density theory is used to calculate the electronic structure associated with impurities and defects in transition metals and their oxides. An embedded molecular cluster scheme is used in which 15–30 atoms are treated explicitly by the LCAO discrete variational scheme, and the surrounding environment is represented by a potential field. One‐electron spectroscopic properties are discussed in terms of densities of states and population analyses; emphasis is placed upon detectable features induced by the presence of defects or impurities. Hyperfine fields and local magnetic moments are examined for binary transition metal alloys, and the effects of local clustering are simulated for comparison with Mössbauer, NMR, and neutron magnetic scattering data. The influence of interstitials and vacancies on metal X‐ray absorption near edge spectra (XANES) of the monoxides is evaluated and used to interpret features of the M_1−xO K edge spectra. The energy of formation of isolated cation vacancies in Fe_1−xO is calculated, and the binding energies of several plausible (m:n) vacancy‐interstitial metal defect clusters are presented. We give some semiquantitative explanations for the relative stability of different defect configurations.