Alloy theory of the intermediate valence state: Application to europium metal

Abstract
A microscopic theory for the intermediate valence state is given, containing no phenomenological parameters. The intermediate state is considered as an alloy of constituents of different integral valence and treated in the virtual-crystal approximation. The theory is applied to europium metal, resulting in a continuous change of valence, starting at 180 kbar and being completed at 350 kbar. The calculated pressured-volume relation resembles those found for some rare-earth monochalcogenides.