First multi-reference correlation treatment of bulk metals

Existence of the sp-d hybridization of the valence band states of the fcc Ca and Sr in the vicinity of the Fermi level indicates that their electronic wave function can have a multi-reference (MR) character. We performed a wave function-based correlation treatment for these materials by means of the method of increments. As oppose to the single-reference correlation treatment (here: coupled cluster), which fails to describe cohesive properties in both cases, employing the MR averaged coupled pair functional one can achieve almost 100 % of the experimental correlation energy.