Cooling rates for Mg and O calculated with a unit particle density (i.e., 1 cm⁻³) for all species, including electrons, and with zero radiation field. Black lines show cooling due to the excited levels listed in the table, red lines show full cooling including ionization from the ground state, and, for comparison, yellow lines show the analogous simulation result with the code CLOUDY from Gnat & Ferland (2012).