  The microcanonical analysis is shown to be a powerful tool to characterize
the protein folding transition and to neatly distinguish between good and bad
folders. An off-lattice model with parameter chosen to represent polymers of
these two types is used to illustrate this approach. Both canonical and
microcanonical ensembles are employed. The required calculations were performed
using parallel tempering Monte Carlo simulations. The most revealing features
of the folding transition are related to its first-order-like character,
namely, the S-bend pattern in the caloric curve, which gives rise to negative
microcanonical specific heats, and the bimodality of the energy distribution
function at the transition temperatures. Models for a good folder are shown to
be quite robust against perturbations in the interaction potential parameters.
