# softmatter:FENE Spring

Finitely extensible non-linear elastic (FENE) springs are often used in bead spring models of polymeric materials.

where *r* is the distance between neighboring beads, *k* is the energy parameter and *R*_{0} is the maximum length of the spring. Typically the values f *k* = 30 and *R*_{0} = 1.5σ are used in simulation, where σ is the diameter of the particle. These values ensure relatively stiff bonds and prevent unphysical chain crossings.

In many simulation packages particle-particle interactions between bonded pairs are not calculated, and thus to avoid particles sitting on top of each other, the Weeks-Chandler-Andersen is often included in the spring potential calculation:

"U"_{WCA} is a Weeks-Chandler-Anderson volume-excluding repulsive force that balances the purely attractive logarithmic term.

## References

- G. S. Grest and K. Kremer, "Molecular dynamics simulation for polymers in the presence of a heat bath," Phys. Rev. A., 33, 3628-3631, (1986)