First principles study of the electronic structures of erbium silicides with non-frozen 4f treatment

The electronic structures (especially 4f states) of hexagonal and tetragonal erbium silicides are investigated within density functional theory. Contrary to previous theoretical studies on these compounds, Er 4f electrons are treated as valence state electrons, explicitly taking into account the on-site Coulomb interactions. Total energy calculations show that the relaxed hexagonal ErSi1.7 is more stable than the tetragonal structure, consistently with related experimental observations. The calculated total density of states of the hexagonal ErSi1.7 agrees well with the experimental valence-band spectrum in a wide energy range from 0 to 12 eV below the Fermi level. In addition, our study indicates that the occupied 4f states in erbium silicides can also locate in the energy range of 0-4.0 eV below the Fermi energy, much different from the prediction of the previously adopted Er ion model.