Photoionization cross sections of neutral atoms (top panel) and their first ionization stage (bottom panel) as functions of the photon energy, derived from the analytical formula of Verner & Yakovlev (1995) (Eq. 1 and Table 1 in their paper). The discontinuities are due to jumps of the cross sections when the photon energy becomes larger than the different thresholds required to extract an electron from internal subshells of the species.