  Accurate ab initio calculations of the energy levels of the superheavy
elements 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.
