Convergence of theab initiomany-body expansion for the cohesive energy of solid mercury

A many-body expansion for mercury clusters of the form E=∑ᵢϵᵢ+∑i<jΔϵᵢⱼ+∑i<j<kΔϵᵢⱼₖ+, does not converge smoothly with increasing cluster size towards the solid state. Even for smaller cluster sizes (up to $n=6$), where van der Waals forces still dominate, one observes bad convergence behavior. For solid mercury the convergence of the many-body expansion can dramatically be improved by an incremental procedure within an embedded cluster approach. Here one adds the coupled cluster many-body electron correlation contributions of the embedded cluster to the bulk HF energy. In this way we obtain a cohesive energy (not corrected for zero-point vibration) of 0.790.3em0exeV in very good agreement with the experimental value of 0.790.3em0exeV.