Statistical mechanics of helical wormlike chains. IV. Persistence vectors

The persistence vector of the helical wormlike chain is defined and evaluated as a function of chain length. It is compared with the persistence vector of a rotational isomeric state model with a determination of the model parameters, taking as examples polymethylene, poly(dimethylsiloxane), isotatic and syndiotactic polystyrene, and isotactic and syndiotactic poly(methylmethacrylate) chains. It is then found that there is good agreement between the persistence vectors of the continuous and discrete models if the directions of the initial tangent and curvature vectors of the former, relative to the first and second bonds of the latter, are chosen properly. The difference between them is at most of the same order of magnitude as the bond length.