In triple-ζ basis sets the artifacts can no longer be ignored. For example, in the full TDKS spectrum computed at the SRC1-r1/6-311++G(d,p) level (Fig. ), it is difficult to tell (in the absence of LR-TDDFT calculations) whether the oxygen K-edge lies at 528 eV or at 532 eV. The peak at 528 eV disappears in the filtered O(1s) spectrum, however, suggesting that this feature is an artifact of N(1s) → continuum transitions. That assignment is confirmed by filtering on the N(1s) orbital, whereas the feature at 511 eV arises from S(2p) orbitals as seen in Fig. . Spectra in Fig. are decomposed into elemental contributions, for calculations using two different basis sets. In each case, the "full" TDKS spectrum is recovered as a sum of contributions from O(1s), N(1s), and S(2p) orbitals, although a very small contribution from S(2s) orbitals is omitted from Fig. , for clarity. Note that relativistic corrections, which are omitted in this work, are much larger for third-row atoms, e.g., 5.9 eV for sulfur 81 versus 0.5 eV for oxygen. If included, these effects would therefore shift the S(2p) feature in Fig. by 5.4 eV but this would not fundamentally alter the picture described here, where transitions to the continuum contaminate spectra at the desired elemental edges, in an erratic manner that is highly sensitive to the choice of basis set.