Although the above expressions correspond to the full EA-TDDFT theory, we apply the TDA throughout this work (i.e. we set B = 0 in Eq. 1). Our use of the TDA is justified by direct comparison with K-edge spectra of NH 3 (aq) computed using the full EA-TDDFT equations in Fig. . Despite the fact that the TDA does not abide strictly by the Thomas-Reiche-Kuhn sum rule, the spectral profiles are unchanged and the excitation energies differ by just 0.001 eV. For K-edge spectra, where an electron is excited from a 1s orbital into a valence virtual orbital, this result makes a great deal of sense because the elements of the B matrix are proportional to the overlap of the donor and acceptor orbitals. Because the elements of B are already nearly zero, the TDA gives results similar to the full EA-TDDFT expressions. Given that the TDA is only a minor approximation in the case of K-edge XAS, we advocate for its use (henceforth implied) within the EA-TDDFT formalism.