FIRST-ORDER PHASE-TRANSITION IN UNFOLDING A COLLAPSED POLYMER - A HISTOGRAM MONTE-CARLO SIMULATION

The phase transition associated with stretching a collapsed polymer ch ain (consisting of N monomers) is investigated in detail using the his togram Monte Carlo simulation method and the bond-fluctuation model. T he distribution functions for the number of contacts and end-to-end di stances an obtained. The free energy profile associated with the trans ition is explicitly computed. Our results on the energy cumulants and free energy profiles provide direct evidence for the first-order natur e of the phase transition. The phase transition occurs in the whole po or solvent regime below the Theta point, chi>chi(c) The free energy ba rrier at the transition is found to scale with N(chi-chi(c)) Phase dia gram for the first-order transition phase boundary is also obtained. W e find that the mean-field theory results give only a qualitatively co rrect picture for the phase transition. [S1063-651X(98)09011-4].