Effect of Non-Pairwise-Additive Interactions on Bundles of Rodlike Polyelectrolytes

Like-charged rigid polyelectrolytes can attract each other due to counterion-mediated interactions to form bundles. However, the resulting effective interactions between rods are not pairwise additive. Here we calculate the free energy of an $N$-rod bundle explicitly. We find that the breakdown of pairwise additivity dramatically affects the stability of bundles of $N$ rods and leads to a barrier in the free energy that grows with increasing salt concentration.