Groupe de Physique Statistique/ Arbeitsgruppe Statistische Physik

The probability that a macromolecular chain occurs in a given conformation is expressed as a product of mean probabilities obtained from Monte Carlo calculations. It permits us to develop a method for the determination of the conformational entropy of chains with long-range interactions. This method has been applied successfully to polymethylene chains with respectively short-range or short-range and hard-sphere interactions. Good results are also obtained for short chains with van der Waals interactions. For the three different potentials used, conformational free energy, energy, and entropy are linear functions of the number of bonds in the chain. The present method gives results in agreement with Monte Carlo sampling when the ratio of the long-range energy to the short-range one is smaller than about 1.5. This method of calculation has also been applied to the determination of chain geometrical dimensions, but it appears that it does not work for that purpose.