The LR-TDDFT formalism has been adapted for the calculation of core excitation spectra using frozen occupied orbitals, equivalent to what is sometimes called the CVS approximation. This corresponds to neglecting amplitudes x ia in Eq. ( ) unless i is a core orbital of interest, e.g., O(1s) or C(1s). Each elemental K-edge is computed separately, using the full virtual space (all ψ a ) but including only the occupied orbitals ψ i for that particular elemental edge. An example for the oxygen K-edge of methionine (Fig. ) demonstrates that this involves negligible approximation, consistent with the general validity of the CVS approximation for K-edge excitations.