FENE

FENE stands for the finitely extensible nonlinear elastic model of a long-chained polymer. It simplifies the chain of monomers by connecting a sequence of beads with nonlinear springs. The spring force law is governed by inverse Langevin function or approximated by the Warner's relationship

${\displaystyle {\textbf {F}}_{i}={\frac {H{\textbf {R}}_{i}}{1-(R_{i}/L_{max})^{2}}}}$

Where ${\displaystyle R_{i}=|{\textbf {R}}_{i}|}$ and H is the spring constant.

Total stretching force on ith bead can be written as: ${\displaystyle {\textbf {F}}_{i}-{\textbf {F}}_{i-1}}$.