Whereas the XA and non-resonant XE are insensitive is insensitive to the choice of delocalized or localized core orbitals when considering simultaneous excitations from all six F1s core orbitals, the parity selection rule is de-cisive in RIXS . In the frame of delocalized core orbitals, the |1t -1 1u 6a 1 1g state has a parity-allowed transition from the ground state and is the sole contributions to the |F1s -1 6a 1 1g resonance in the XA spectrum, since neither 2a -1 1g 6a 1 1g and |1e -1 g 6a 1 1g can be reached within the dipole approximation.