The cohesive energy of superheavy element copernicium determined from accurate relativistic coupled-cluster theory

The cohesive energy of bulk copernicium is accurately determined using the incremental method within a relativistic coupled-cluster approach. For the lowest energy structure of hexagonal close-packed (hcp) symmetry, we obtain a cohesive energy of −36.3 kJ mol−1 (inclusion of uncertainties leads to a lower bound of −39.6 kJ mol−1), in excellent agreement with the experimentally estimated sublimation enthalpy of −38+12−10 kJ mol−1 [R. Eichler et al., Angew. Chem. Int. Ed., 2008, 47, 3262]. At the coupled-cluster singles, doubles and perturbative triples level of theory, we find that the hcp structure is energetically quasi-degenerate with both face-centred and body-centred cubic structures. These results provide a basis for testing various density-functionals, of which the PBEsol functional yields a cohesive energy of −34.1 kJ mol−1 in good agreement with our coupled-cluster value.