  We use the recently developed soft-potential-enhanced Poisson-Boltzmann (SPB)
theory to study the interaction between two parallel polyelectrolytes (PEs) in
monovalent ionic solutions in the weak-coupling regime. The SPB theory is
fitted to ion distributions from coarse-grained molecular dynamics (MD)
simulations and benchmarked against all-atom MD modelling for
poly(diallyldimethylammonium) (PDADMA). We show that the SPB theory is able to
accurately capture the interactions between two PEs at distances beyond the PE
radius. For PDADMA positional correlations between the charged groups lead to
locally asymmetric PE charge and ion distributions. This gives rise to small
deviations from the SPB prediction that appear as short-range oscillations in
the potential of mean force. Our results suggest that the SPB theory can be an
efficient way to model interactions in chemically specific complex PE systems.
