Ultraviolet inverse photoemission from iron monoxide and self-interaction-corrected local-spin-density calculations.

Abstract

We present inverse photoemission (IP) results from ${\mathrm{Fe}}_{\mathit{x}}$O taken in the isochromat mode at a variety of photon energies in the ultraviolet (11.5--23-eV) and the FeO partial and total density of states calculated in the self-interaction-corrected--local-spin-density approximation (SIC-LSD). The measurements show the Fe 3d contribution just above the bottom of the conduction band ${\mathit{E}}_{\mathit{c}}$ and point out a contribution of the type ${\mathit{d}}^{8}$L (L denotes ligand hole) 12 eV above ${\mathit{E}}_{\mathit{c}}$; this is superimposed on oxygen (p)-derived states. The comparison with IP and with available direct photoemission results shows the advantages of SIC-LSD over LSD: in particular, the calculations give a gap and account for a distribution of the Fe 3d character in a wide energy range (15 eV) in the ground state. Moreover, the comparison with the experiment shows that SIC-LSD gives a satisfactory approximate evaluation of the Coulomb energy U and of the charge-transfer energy \ensuremath{\Delta} to be used in an impurity model to treat the spectral features that cannot be described by the SIC-LSD eigenvalues (${\mathit{d}}^{6}$L and ${\mathit{d}}^{8}$L final states in direct and inverse photoemission, respectively).