Accurate ab initio calculations of the energy levels of the superheavy element $Z=112$ are presented. Relativistic Hartree-Fock and configuration interaction methods are combined with the many-body perturbation theory to construct the many-electron wave function for valence electrons and to include core-valence correlations. Two different approaches in which the element is treated as a system with two or twelve external electrons above closed shells are used and compared. Similar calculations for mercury are used to control the accuracy of the calculations. The results are compared with other calculations.

• Received 14 October 2008

DOI:https://doi.org/10.1103/PhysRevA.78.062502