Module torsion 

Dihedral Torsion Potentials

Four-body potentials for dihedral angle rotation.

Included Potentials

Potential	Description	Common Use
Cos	Periodic cosine	AMBER, DREIDING
Opls	Fourier series	OPLS
Rb	Ryckaert-Bellemans	GROMOS
Harm	Harmonic	Restraints

Dihedral Convention

For atoms i-j-k-l:

• phi is the angle between planes (i,j,k) and (j,k,l)
• phi = 0 when all four atoms are in the same plane (cis configuration)
• phi = 180° for trans configuration

The sign convention follows the IUPAC definition:

• Looking along j->k, phi is positive for clockwise rotation of l relative to i

Example

use potentials::torsion::{Cos, Potential4};

// Ethane-like torsion: barrier = 2.5 kcal/mol, 3-fold symmetry
let torsion = Cos::new(2.5, 3, 0.0);

let phi = std::f64::consts::PI / 3.0; // 60 degrees
let (cos_phi, sin_phi) = (phi.cos(), phi.sin());
let energy = torsion.energy(cos_phi, sin_phi);

Re-exports

pub use crate::base::Potential4;

Structs

Cos

Periodic cosine torsion potential.

Harm

Harmonic torsion potential (restraint).

Opls

OPLS Fourier series torsion potential.

Rb

Ryckaert-Bellemans torsion potential.