  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.
