Importantly, no additional SCF cycles should be performed on the ionized core-hole reference state, if it is read in from a separate job between steps 2 and 3. (Additional Roothaan steps are sometimes used to ensure the consistency of the Fock and density matrices for a set of input orbitals, but in the present context this spoils the core-hole reference state and degrades the quality of the XES spectra simulated using TD-DFT.) This approach corresponds to a "sudden" approximation, in which MOs for the neutral molecule are used to describe the ionized core-hole state.