Transition energies of mercury and ekamercury (element 112) by the relativistic coupled-cluster method

The relativistic coupled-cluster method is used to calculate ionization potentials and excitation energies of Hg and element 112, as well as their mono- and dications. Large basis sets are used, with l up to 5, the Dirac-Fock or Dirac-Fock-Breit orbitals found, and the external 34 electrons of each atom are correlated by the coupled-cluster method with single and double excitations. Very good agreement with experiment is obtained for the Hg transition energies, with the exception of the high (12 eV) excitation energies of the dication. As in the case of element 111 [Eliav et al., Phys. Rev. Lett. 73, 3203 (1994)], relativistic stabilization of the 7s orbital leads to the ground state of 112+ being 6d97s2, rather than the d10s ground states of the lighter group 12 elements. The 1122+ ion shows very strong mixing of the d8s2, d9s, and d10 configurations. The lowest state of the dication is 6d87s2 J=4, with a very close (0.05 eV) J=2 state with strong d8s2 and d9s mixing. No bound states were found for the anions of the two atoms.