Hole localization and symmetry breaking

A brief overview is presented of some theoretical work on the symmetry breaking of electronic wavefunctions that followed the early work on Bagus and Schaefer who observed that a considerable lower SCF energy could be obtained for an ionized state of the O2 molecule with a 1s hole if the symmetry restrictions were released, so that the core hole could localize on one of the two oxygens. In the present contribution some emphasis is put on the properties of symmetry adapted wavefunctions, which are obtained through a nonorthogonal CI amongst different symmetry broken wave functions. n-π* Excited states of para-benzoquinone and 3d-σ ionized states of Cu2 are used as illustrative examples