Struct Harmonic 

pub struct Harmonic;

Harmonic potential implementation for 1-2 bond stretching.

Physics

Models the bond stretching as a harmonic oscillator.

• Formula: $$ E = \frac{1}{2} K (R - R_0)^2 $$
• Derivative Factor (diff): $$ D = -\frac{K (R - R_0)}{R} $$

Parameters

• k_half: Half force constant $K_{half} = K/2$.
• r0: Equilibrium distance $R_0$.

Inputs

• r_sq: Squared distance $r^2$ between two atoms.

Implementation Notes

• Requires square root to obtain $R$.
• All intermediate calculations are shared between energy and force computations.
• Branchless and panic-free.

Trait Implementations

impl Clone for Harmonic

fn clone(&self) -> Harmonic

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Harmonic

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Harmonic

fn default() -> Harmonic

Returns the “default value” for a type.

impl<T: Real> PairKernel<T> for Harmonic

fn energy(r_sq: T, (k_half, r0): Self::Params) -> T

Computes only the potential energy.

Formula

$$ E = K_{half} (R - R_0)^2 $$

fn diff(r_sq: T, (k_half, r0): Self::Params) -> T

Computes only the force pre-factor $D$.

Formula

$$ D = -\frac{2 K_{half} (R - R_0)}{R} $$

This factor is defined such that the force vector can be computed by a single vector multiplication: $\vec{F} = -D \cdot \vec{r}$.

fn compute(r_sq: T, (k_half, r0): Self::Params) -> EnergyDiff<T>

Computes both energy and force pre-factor efficiently.

This method reuses intermediate calculations to minimize operations.

type Params = (T, T)

Associated constants/parameters required by the potential (e.g., $k, r_0$).

impl Copy for Harmonic