Orientational correlation function and persistence lengths of flexible polyelectrolytes

Orientational correlation functions have been obtained from Monte Carlo simulations of long, freely jointed chains (1000 monomers and more) with screened Coulomb interactions truncated after a certain number of bonds. This makes it possible to study chain-length dependence without end effects and to display excluded-volume effects. These correlation functions form the basis for a discussion of the conformational response to electrostatic interactions. In particular, they are related to the concept of electrostatic persistence length and the correlation functions illustrate the differences between different definitions of persistence length. To facilitate future discussions, we have identified four types of definitions and given them separate names: (1.) projection length, which involves: integration of the orientational correlation function; (2) orientational correlation length, which is the decay length of an exponential function; (3) bending coefficient, which is a length representing a bending force constant; and (4) crossover distance, which is the monomer-monomer distance at the boundary between a rodlike and a swollen behavior. Previous conclusions that the projection length obeys a power law at high salt concentrations, while the orientational correlation length does not, are confirmed. Furthermore, a power law is also found in the salt-free limit for the projection length corresponding to an infinite chain with a finite range of interactions. The two power laws make it possible to construct a universal curve that gives an almost quantitative description of the chain behavior.