  We investigate knotting probabilities of long double-stranded DNA strands in
a coarse-grained Kratky-Porod model for DNA with Monte Carlo simulations.
Various ionic conditions are implemented by adjusting the effective diameter of
monomers. We find that the occurrence of knots in DNA can be reinforced
considerably by high salt conditions and confinement between plates. Likewise,
knots can almost be dissolved completely in a low salt scenario. Comparisons
with recent experiments confirm that the coarse-grained model is able to
capture and quantitatively predict topological features of DNA and can be used
for guiding future experiments on DNA knots.
