From the van der Waals dimer to the solid state of mercury with relativistic ab initio and density functional theory

A comprehensive study of small mercury clusters is presented using relativistic coupled cluster, many-body perturbation, and density functional theory starting from the dimer potential, to small clusters and to the solid state. In all these calculations we employ an energy-consistent small core relativistic pseudopotential. We address the possibilities for the simulation of larger clusters. Both Lennard-Jones and alternative isomers are considered as candidate structures for the global minimum, and both isotropic and anisotropic polarizabilities are determined for N <= 24. We address the well-known nonconvergence of the many-body expansion of the interaction potential. We show that a two-body potential cannot describe the rhombohedral distortion from a face centered cubic structure. Density functional theory seems to have similar difficulties with the exception of the local density approximation. We therefore suggest a two-body correlation potential to be used to correct the Hartree-Fock energy, which already contains the important many-body effects. Within this approach we obtain good agreement with the best-known reference data ranging from the dimer to the solid state.