Journal of Chemical Theory and Computation
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Calculation of vertical excitation energies by the adiabatic linear-response time-dependent density-functional theory (TDDFT) requires static Kohn–Sham potentials and exchange–correlation kernels. When these quantities are derived from standard density-functional approximations (DFA), mean absolute errors (MAE) of the method are known to range from 0.2 eV to over 1 eV, depending on the functional and type of excitation. We investigate how the performance of TDDFT varies when increasingly accurate exchange–correlation potentials derived from Hartree–Fock (HF) and post-HF wavefunctions are combined with different approximate kernels. The lowest MAEs obtained in this manner for valence excitations are about 0.15–0.2 eV, which appears to be the practical limit of the accuracy of TDDFT that can be achieved by improving the Kohn–Sham potentials alone. These findings are consistent with previous reports on the benefits of accurate exchange–correlation potentials in TDDFT, but provide new insights and afford more definitive conclusions.