Rare earths presenting strong f-d hybridization

A large similarity in electronic behaviour between rare earths and actinides can be found for the first and the last elements of the rare earths series where a strong f-d interaction is found near the Fermi level. We have selected TmSe and Ce as particular examples to study this problem. To study the changes in the electronic structure of thulium selenide we used an octahedral cluster with the rare earth atom sitting at the center. The changes in the lattice parameters were simulated changing the volume per cluster and the interatomic distances. To study the FCC cerium electronic transitions we used a 6-atoms cluster with α-cerium lattice parameters. The clusters are embedded in a potential representing the medium. In both cases we found a large instability of the part of the f-band near the Fermi level which becomes more hybridized with the d-band on decreasing the lattice parameter. In cerium the f-resonance is not lost but above the Fermi level; because of the broadening of the f-band, the electrons, holes, become much less localized. This behaviour can be used to understand the change in magnetic properties in terms of this qualitative change of the character of the f-d electronic bands. A detailed description of the s, p, d and f electrons is presented. (orig./GSCH)