The behavior of f-levels in HCP and BCC rare-earth elements in the ground state and in XPS and BIS spectroscopy from density-functional theory
The electronic structures of rare-earth elements in the HCP structure, and Europium in the BCC structure, are calculated by use of density-functional theory, DFT. Simulation of X-ray photoemission spectroscopy (XPS) and bremsstrahlung isochromatic spectroscopy (BIS) are made within DFT by imposing that f-electrons are excited by a large photon energy, either by removing from the occupied states in XPS, or by adding to the unoccupied f-states in BIS. The results show sizable differences in the apparent position of the f-states compared to the f-band energy of the ground states. This result is fundamentally different from calculations assuming strong on-site correlation since all calculations are based on DFT. Spin-orbit coupling and multiplet splittings are not included. The present simulation accounts for almost half of the difference between the f-level positions in the DFT ground states and the observed f-level positions. The electronic specific heat at low T is compatible with the DFT ground state, where f-electrons often reside at the Fermi level.