Symmetry Breaking and Self-Interaction Correction in the Chromium Atom and Dimer*

Owing to its complex electronic structure and unusual sextuple bond, the chromium dimer has remained a challenging molecule to describe within density functional theory (DFT). In this talk, we present a new but apparently unphysical symmetry-broken solution for the dimer in self-interaction-corrected DFT that is stabler than the routinely reported antiferromagnetic ground state by more than 4 eV. The net moment on each chromium atom is close to zero and this is consistent with a sextuply-bonded molecule. A similar form of symmetry-breaking is observed for the chromium atom, and it is suggested that either complex localized orbitals and/or modifications to the self-interaction correction in many-electron regions might be needed to properly describe the Cr atom and dimer.