Strategy for an evaluation of core excitation energies in complex molecules: application to SF6

Modelling of single core-hole states is proposed, which consists of adding an external charge exerting on the remaining electrons to an outer repulsion globally equivalent to the inner attraction resulting from the partial unscreening of the nucleus. For a given complex molecule and an ionized core level, this outer equivalent charge (oech), which may be fractional, can be computed by comparing results from exact core-hole calculations and from applying Koopmans' theorem to valence-ion results for a related simpler molecule. For double core-hole states, the total relaxation energy is computed by adding to the single relaxation energies an induced relaxation energy approximated by the geometric average of the former. This model helps to assign two satellites in the photoelectron spectrum of SF₆ to singlet and triplet double core-hole states.