Conformations and tangent correlations from coil to rod
The worm-like chain (WLC) model describes semiflexible polymers (DNA, actin, microtubules).
Each segment has bending energy κ·(Δθ)²/2. Tangent-tangent correlation: ⟨t(s)·t(0)⟩ = exp(−s/Lp).
When L≪Lp the chain is rod-like; when L≫Lp it forms a random coil with ⟨R²⟩ = 2LpL.