Electronic structure of Mn and Fe oxides

We present a clear, simple tight-binding representation of the electronic structure and cohesive energy (energy of atomization) of MnO, Mn$_{2}$O$_{3}$, and MnO$_{2}$, in which the formal charge states Mn$^{2+}$, Mn$^{3+}$, and Mn$^{4+}$, respectively, occur. It is based upon localized cluster orbitals for each Mn and its six oxygen neighbors. This approach is fundamentally different from local-density theory (or LDA+U), and perhaps diametrically opposite to Dynamical Mean Field Theory. Electronic states were calculated self-consistently using existing parameters [1], but it is found that the charge \textit{density} is quite insensitive to charge \textit{state}, so that the starting parameters are adequate. The cohesive energy per Mn is dominated by the transfer of two $s$ electrons to oxygen $p$ states, the same for all three compounds. The differing transfer of majority $d$ electrons to oxygen $p$ states, and the coupling between them, accounts for the observed variation in cohesion in the series. The same description applies to the perovskites, such as La$_{x}$Sr$_{1-x}$MnO$_{3}$, and can be used for FeO, Fe$_{2}$O$_{3}$ (and FeO$_{2})$, Because the formulation is local, it is equally applicable to impurities, defects and surfaces. \newline [1] Walter A. Harrison, \textit{Elementary Electronic Structure,} World Scientific (Singapore, 1999), revised edition (2004).