Function compute_hf3c 

pub fn compute_hf3c(
    elements: &[u8],
    positions: &[[f64; 3]],
    config: &HfConfig,
) -> Result<Hf3cResult, String>

Run a complete HF-3c calculation (Hartree-Fock with D3, gCP, SRB corrections).

elements: atomic numbers. positions: Cartesian coordinates in Å, one [x,y,z] per atom. config: calculation parameters (or use HfConfig::default()).

Returns orbital energies, total energy, correction energies, and optional CIS states.