  We perform a generalized-ensemble simulation of a small peptide taking the
interactions among all atoms into account. From this simulation we obtain
thermodynamic quantities over a wide range of temperatures. In particular, we
show that the folding of a small peptide is a multi-stage process associated
with two characteristic temperatures, the collapse temperature T_{\theta} and
the folding temperature T_f. Our results give supporting evidence for the
energy landscape picture and funnel concept. These ideas were previously
developed in the context of studies of simplified protein models, and here for
the first time checked in an all-atom Monte Carlo simulation.
