Monte Carlo study of the phase structure of compact polymer chains

We study the phase behavior of single homopolymers in a simple hydrophobic/ hydrophilic off-lattice model with sequence independent local interactions. The system size dependence of the specific heat at low temperatures is inv estigated using chains with up to 50 monomers. Our calculations are perform ed using the methods of simulated and parallel tempering. The performances of these algorithms are discussed, based on careful tests for a small syste m.