A short CI expansion for a symmetry-adapted description of localized hole states: Application to the 3dσu hole state of the Cu2 + ion

A simple formalism is developed to describe by means of a symmetry-adapted wavefunction the localized hole states which may arise in symmetric systems. A short CI expansion is generated in a systematic way from the delocalized molecular orbitals of the SCF ground state. For the 3dσ_u hole state of the _Cu2 ⁺ ion, the symmetry adapted and the broken symmetry solutions approximately correspond to the same energy at that level of CI.