  The electronic structures of ABO3 ferroelectrics are calculated within the
density functional theory, and their evolution is analyzed as the crystal-field
symmetry changes from cubic to rhombohedral via tetragonal phases. Electronic
structure fingerprints that characterize each phase from their electronic
spectra are identified. We carried out electron-energy loss spectroscopy
experiments by using synchrotron radiation and compared these results to the
theoretical spectra calculated within DFT-LDA. The dominant role of the BO6
octahedra in the formation of the energy spectra of ABO3 compounds was
demonstrated. Anomalous behavior of plasmons in ferroelectrics was exhibited by
the function representing the characteristic energy loss in the region of phase
transition.
