Comparison between the X-ray atomic database of SPEX (red) and Schippers et al. (2021; black) for Fe I, Fe II, Fe III, and Fe IV. The Fe I, Fe II, and Fe IV data in Schippers et al. (2021) have been taken from Richter et al. (2004), Schippers et al. (2017), and Beerwerth et al. (2019), respectively.