  We present results of molecular dynamics simulations of strong, flexible
polyelectrolyte chains in solution with added salt. The effect of added salt on
the polyelectrolyte chain structure is fully treated for the first time as a
function of polymer density. Systems above and below the Manning condensation
limit are studied. The chain contraction due to added salt is weaker than
expected from simple screening arguments. The chain structure is intimately
tied to the ion density near the chain even for chains in the counterion
condensation regime. In contradiction to Manning counterion condensation
theory, the ion density near the polymer chain depends on the amount of added
salt, and above the condensation limit the chains significantly contract due to
added salt.
