Natural localized orbitals At a high level, the natural bond orbital (NBO) analysis provides electron density information, providing a valid description of a molecule's wave function. Instead of representing these densities as delocalized molecular orbitals, this method yields a collection of localized natural atomic orbitals, hybrid orbitals, and bond orbitals. Moreover, NBO analysis expresses interactions between filled orbitals (donors) and empty orbitals (acceptors).