Function calculate_dihedral 

pub fn calculate_dihedral(
    geometry: &Geometry,
    a1: usize,
    a2: usize,
    a3: usize,
    a4: usize,
) -> f64

Calculate the dihedral angle between four atoms in radians.

The dihedral angle is computed using the atan2 method for proper sign. The angle is in the range (-π, π].

Arguments

• geometry - The molecular geometry containing atomic positions.
• a1 - Index of the first atom (0-based).
• a2 - Index of the second atom.
• a3 - Index of the third atom.
• a4 - Index of the fourth atom.

Returns

The dihedral angle in radians. Returns 0.0 for degenerate cases.