The conformational statistics of polymer chains as obtained from their energy landscape: a conceptual view of the rotational isomeric state approach

Abstract

In the rotational isomeric state (RIS) approach the conformational statistics of a polymer chain can be conveniently described in terms of the statistical matrix. In this work it is shown from a conceptual point of view to which degree the projection onto a few states, inherently present in any RIS approach, may lead to systematic deviations for estimation of the a priori probabilities. It is shown that these deviations scale with some power of the inverse temperature. Furthermore an algorithm is presented, deriving the statistical matrix from computer simulations. This algorithm is applied to polyethylene. Comparison with the conformational statistics as obtained from Monte Carlo simulations allows the quality of the statistical matrix elements to be estimated. It turns out that the systematic deviation does not hamper practical applications. Questions like the relevance of the anharmonicity of the energy landscape or consideration of more than nearest-neighbor correlations in the RIS approach are discussed.