The structures of CaC and Ca2Cin the light of the Extended Zintl-Klemm Concept

The structures of Ca2C and CaC, recently predicted from evolutionary algorithms to be stable at very high pressures, are rationalized on the basis of the structural transitions undergone by calcium under pressure as well as in the light of the Extended Zintl-Klemm Concept that serve as a guide to explain the structures.