Struct FreelyJointedChain 

pub struct FreelyJointedChain {
    pub n_segments: f64,
    pub kuhn_length: f64,
    pub temperature: f64,
}

Freely Jointed Chain polymer model.

Models a polymer as N rigid segments of length b (Kuhn length), with free rotation about each joint.

Fields

n_segments: f64

Number of Kuhn segments

kuhn_length: f64

Kuhn segment length [m]

temperature: f64

Temperature [K]

Implementations

impl FreelyJointedChain

pub fn new(n_segments: f64, kuhn_length: f64, temperature: f64) -> Self

Create a new Freely Jointed Chain model.

Arguments

• n_segments - Number of Kuhn segments N
• kuhn_length - Kuhn length b [m]
• temperature - Temperature [K]

pub fn mean_square_end_to_end(&self) -> f64

Mean square end-to-end distance: R² = N * b².

pub fn rms_end_to_end(&self) -> f64

RMS end-to-end distance: R²^(1/2) = b * sqrt(N).

pub fn contour_length(&self) -> f64

Contour length: L_c = N * b.

pub fn inverse_langevin(x: f64) -> f64

Inverse Langevin function approximation (Padé approximant).

L_inv(x) ≈ x * (3 - x²) / (1 - x²) for |x| < 1.

pub fn force_extension(&self, extension: f64) -> f64

Force-extension relationship: F = (kT/b) * L_inv(R/L_c).

Arguments

• extension - End-to-end distance R [m], must be < contour length

pub fn spring_constant(&self) -> f64

Entropic spring constant at small extensions: k = 3kT / (N*b²).