Energy structure and optical spectra FeBO3 with account of strong electronic correlations

The model of the FeBO3 structure, combining the single-electron description of the boron and oxygen sp-states and multielectron description of the iron d--states is proposed. The exact Leman spectral representation is applied for calculating the Green function of the d-electrons; the energies of the d-type quasi-particles are calculated through the terms of the d4, d5 and d6 configurations. The optical absorption spectrum is determined by the local excitons and electron excitations with the charge transfer; the latter ones determine the nature of the dielectric gap in the FeBO3. The model parameters are obtained from the comparison with the excitons energy; the single-particle density for the FeBO3 states is calculated; the basic lines in the optical absorption spectrum agree well with the experimental data up to the 3 eV energies