Averaged coupled pair functional structure

In contrast to spherical ions, a proper evaluation of the static structure factor for rod-like polyions by means of pair distribution functions is not available so far. As mentioned earlier, the difficulty arises from the coupling of the form factor and structure factor, i.e., the orientation of the rods depends on the position and orientation of the neighbouring rods. The distribution function for rod-like particles may be written as g(r, Ui, Uj) which indudes both the rod-to-rod distance r and the mutual orientation of two rods given by the vectors Ui and Uj [35]. From this distribution function the averaged distribution function g(r), the analog to g(r) in the case of spherical ions, and the structure factor S(q) are principally accessible. 

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