Orbital (2nd order) interactions These represent the interactions between donor and acceptor orbitals. Donors, represented by lone pairs n, σ, and π bonds, are electron-rich orbitals, while acceptors, represented by σ * , and π * anti-bonds are electron deficient. In practical terms, our ground truth graph represents one donor-acceptor interaction as a connection between the respective nodes. The NBO analysis quantified these interactions by the perturbation energy, energy difference, and the Fock matrix element, totalizing three targets.