Localized 4f-states

A review paper by Osterwalder (1985) on the photoemission (both XPS and UPS) and inverse photoemission (BIS) results for Y, La, Ce, Pr and their hydrides includes extensive references. XPS valence-band spectra for the metals and hydrides are shown in fig. 18. The common features for all the systems are clear however, XPS instruments cannot resolve the f-peaks as well as UPS spectrometers. A very important point discussed by Osterwalder is the concept of hybridization, particularly with the supposedly localized 4f states. The overlap of appropriate symmetries and energies can result in a complex picture, particularly in the generation of low-lying states that are... 

A general picture of the valence electronic structure of compounds of rare earths (which are early transition metals) and late 3d transition metals is shown in fig. 40, where the localized 4f states are not included. The lanthanide (R) contributes 5d, 6s and 6p valence states and the 3d transition metal (M) contributes 3d, 4s and 4p states. Since in the solid the s and p projected orbitals will form broad and rather feature-less free-electron bands, these may be neglected as a first approximation, leaving the 5d and 3d states. In the free atom the energy of the M 3d states lies far lower than that of the R 5d states, as shown on the left in fig. 40. The first... 

The effects of the localized 4f moments on the band structure have been studied in detail for the RFe2 (Brooks et al. 1991a, b) and RC02 (Nordstrom et al. 1991a, b) series by treating the localized 4f states as outer core states. This is done in order to fix the number of 4f electrons to an integer, as in the inlinite-t/ limit of the Hubbard model (Hubbard 1963). Again the number of spin-up and spin-down 4f electrons is an input to the calculation, but, subject to this constraint, the 4f spin densities are calculated self-consistently. The 4f spin densities contribute to the total spin densities. 

A semiconductor-to-metal transition results, and approximately 10 electrons per cm are released from the localized 4f state into the conducting 5d state. This valence change and 4f electron delocalization occurs in SmS near 7000 bar. The electrical conductivity of SmS abruptly increases at the transition pressure as would be... 

---