THE CONFORMATIONAL STATISTICS OF POLYMER-CHAINS AS OBTAINED FROM THEIR ENERGY LANDSCAPE - A CONCEPTUAL VIEW OF THE ROTATIONAL ISOMERIC STATE APPROACH

In the rotational isomeric state (RIS) approach the conformational sta tistics of a polymer chain can be conveniently described in terms of t he statistical matrix. In this work it is shown from a conceptual poin t of view to which degree the projection onto a few states, inherently present in any RIS approach, may lead to systematic deviations for es timation of the a priori probabilities. It is shown that these deviati ons scale with some power of the inverse temperature. Furthermore an a lgorithm is presented, deriving the statistical matrix from computer s imulations. This algorithm is applied to polyethylene. Comparison with the conformational statistics as obtained from Monte Carlo simulation s allows the quality of the statistical matrix elements to be estimate d. It turns out that the systematic deviation does not hamper practica l applications. Questions like the relevance of the anharmonicity of t he energy landscape or consideration of more than nearest-neighbor cor relations in the RIS approach are discussed.