# Topo2 implementation into LAMMPS with external code
We model a torsionally relaxed (nicked) DNA plasmid 7.2 kbp-long as a bead-spring polymer made of 1000 beads with bead-size σ=2.5 nm=7.3 bp and connected by finitely extensible springs. The persistence length of the polymer is set to lp = 50 nm. Beads interact via a purely
steric Lennard-Jones repulsion while the TopoII-bound segment is modelled as a 50 beads (L=360 bp)-long segment displaying soft interactions with the other beads thereby allowing the TopoII-bound segment to undergo strand-crossing with a small energy penalty (2 kBT). For details in the model and the system used we refer the reader to our paper: ***D. Michieletto, et al. "Dynamic and Facilitated Binding of Topoisomerase Accelerates Topological Relaxation"***
steric Lennard-Jones repulsion while the TopoII-bound segment is modelled as a 50 beads (L=360 bp)-long segment displaying soft interactions with the other beads thereby allowing the TopoII-bound segment to undergo strand-crossing with a small energy penalty (2 kBT). For details in the model and the system used we refer the reader to our paper: ***D. Michieletto, et al. "Dynamic and Facilitated Binding of Topoisomerase Accelerates Topological Relaxation"***.
The position of the TopoII-bound segment can be either:
