At high temperature, , the assumption of non-relativistic
electron velocities becomes invalid, and a variety of physical processes
such as electron-positron pair production may come into play. At very
low temperatures,
, many of the analytic fitting formulae
used to parameterize atomic rates are unreliable, and
the neglect of molecule formation and atomic fine structure cooling renders
rates inaccurate. The code does not allow temperatures less than
3000K for this reason and because serious numerical errors can occur.
If lower values are attempted the temperature is artificially reset to 3000K.
On the high temperatures end, there is no mechanism preventing
values greater than
, but the user should be aware that in this
regime the rates are probably unreliable.