Evolution of the ion abundance as a function of the H₂ number density for the fiducial model at times of, from top right to bottom left, 1 Myr, 3 Myrs, 9 Myrs, and 11.3 Myrs. The black line represents the abundance-density relation at the center of the cloud for the entire duration of the simulation, the red points correspond to the ionization fraction from all cells in the domain at the specific point in time, and the blue dashed lines represent the power law that best fits the abundance-density relation at that point in time.