Ab initio theory of valency in ytterbium compounds

The electronic structure of 26 Yb compounds is calculated with the ab initi o self-interaction-corrected local-spin-density approximation. In this appr oach 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 t he remaining 14th f electron giving rise to a very narrow f resonance, whic h straddles the Fermi energy. The systems studied comprise the Yb monopnict ides and monochalcogenides as well as a series of intermetallic compounds. Experimental equilibrium volumes are well reproduced. The results provide q uantitative support to the experimental classification of Yb compounds in t erms of effective valencies.