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 R0 is the maximum length of the spring. Typically the values f k = 30 and R0 = 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.
- 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)