// Create a `OrbitalIntegral` instance to store a two-electron molecular // orbital integral data. var twoElectronIntegral = new OrbitalIntegral(new[] { 0, 1, 2, 3 }, 0.123); // This enumerates all spin-orbital indices of the `FermionTerm`s in the // Hamiltonian represented by this integral -- this is an array of array // of `SpinOrbital` instances. var twoElectronSpinOrbitalIndices = twoElectronIntegral.EnumerateSpinOrbitals();