Ab initiotheory of valency in ytterbium compounds

The electronic structure of 26 Yb compounds is calculated with the ab initio self-interaction-corrected local-spin-density approximation. In this approach f electrons can be described as either localized or delocalized. Hence a divalent Yb ion is represented with a completely localized $f^{14}$ shell, while a trivalent Yb ion is represented with a localized $f^{13}$ shell with the remaining $14\mathrm{th}$ f electron giving rise to a very narrow f resonance, which straddles the Fermi energy. The systems studied comprise the Yb monopnictides and monochalcogenides as well as a series of intermetallic compounds. Experimental equilibrium volumes are well reproduced. The results provide quantitative support to the experimental classification of Yb compounds in terms of effective valencies.