The atomic rates for H and He-like ions are accurate for
densities up to cm by taking into account the effects of 3-body
recombination and lowering of the continuum ([Bautista et al.
1998], [Bautista et al. 1999]). However, these effects are not
treated for other species which reduce the accuracy of the model
results for these ions at high density. The density for which
these effects become important for a given ion increases rapidly
with effective charge of the ion, starting at about cm for z=1
and at about cm for z=8. At low densities numerical errors can
occur; the user is urged to read chapter 6.