Struct Coulomb 

pub struct Coulomb;

Standard Coulomb potential implementation for electrostatics.

Physics

Models the electrostatic interaction between two point charges.

• Formula: $$ E = \frac{C \cdot q_i q_j}{\epsilon \cdot r} $$
• Derivative Factor (diff): $$ D = -\frac{1}{r} \frac{dE}{dr} = \frac{E}{r^2} = \frac{C \cdot q_i q_j}{\epsilon \cdot r^3} $$

Parameters

• q_product: The effective charge product $ Q_{eff} = \frac{C \cdot q_i q_j}{\epsilon} $.

Inputs

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

Implementation Notes

• Optimized to minimize arithmetic operations by reusing intermediate inv_r and inv_r2.
• Utilizes rsqrt for potential hardware acceleration.
• Branchless and panic-free.

Trait Implementations

impl Clone for Coulomb

fn clone(&self) -> Coulomb

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Coulomb

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

Formats the value using the given formatter.

impl Default for Coulomb

fn default() -> Coulomb

Returns the “default value” for a type.

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

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

Computes only the potential energy.

Formula

$$ E = \frac{Q_{eff}}{r} $$

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

Computes only the force pre-factor $D$.

Formula

$$ D = \frac{Q_{eff}}{r^3} $$

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, q_product: Self::Params) -> EnergyDiff<T>

Computes both energy and force pre-factor efficiently.

This method reuses intermediate calculations to minimize operations.

type Params = T

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

impl Copy for Coulomb