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The free energy of knots 71 and 10151 as a function of their sizes, S. The linear chain containing a chosen knot was stretched by a small force of 0.05 pN. The umbrella sampling was used in the Monte Carlo simulation to obtain G(S) over the wide range of S (see Methods). The broad minimum of G(S) seen for both knots is due to the small stretching force (of 0.05 pN) applied to the chain ends.
