The bond length and dissociation energy of the Copernicium dimer calculated at different levels of theory are presented. The coupled-cluster and the density functional method are used in fully relativistic four-component all-electron calculations and two-component calculations using effective core potentials, which include the Breit contribution and quantum electrodynamic effects. The results show the importance of the spin-orbit coupling and also the Gaunt/Breit contribution, which could be easily included in the pseudopotential calculations. Additionally, a reversal in the trend of the bonding of the group 12 dimers could be shown by analyzing the charge fluctuation and local spin expectation values. (C) 2014 Elsevier B.V. All rights reserved.