<p>We thoroughly benchmark
time-dependent density- functional theory for the predictive calculation of
UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach
that is computationally feasible for large-scale applications such as
biological systems or molecular framework materials, albeit performing with
high accuracy for the Q-bands, we compare the results given by various computational
protocols, including basis sets, density-functionals (including gradient
corrected local functionals, hybrids, double hybrids and range-separated
functionals), and various variants of time-dependent density-functional theory,
including the simplified Tamm-Dancoff approximation. An excellent choice for
these calculations is the range-separated functional CAM-B3LYP in combination
with the simplified Tamm-Dancoff approximation and a basis set of double-ζ
quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed
by more expensive approaches, not even by double hybrid functionals, and solely
systematic excitation energy scaling slightly improves the results (MAE ~0.04
eV). </p>
