We study the phase behavior of single homopolymers in a simple hydrophobic/
hydrophilic off-lattice model with sequence independent local interactions.
The specific heat is, not unexpectedly, found to exhibit a pronounced peak
well below the collapse temperature, signalling a possible low-temperature
phase transition. The system size dependence at this maximum is investigat
ed both with and without the local interactions, using chains with up to 50
monomers. The size dependence is found to be weak. The specific heat itsel
f seems not to diverge. The homopolymer results are compared with those for
two nonuniform sequences. Our calculations are performed using the methods
of simulated and parallel tempering. The performances of these algorithms
are discussed, based on careful tests for a small system. (C) 1999 American
Institute of Physics. [S0021-9606(99)51224-5].