Instead of the simplest free-electron-gas approximation via the eq. 74, FOs of cumulene and polyyne can be, in principle, approached by using the Dirac-Kronig-Penney model described in section 3.6. The only difference would be that for cumulene, we start with the equally-spaced lattice of Dirac deltas, whereas for polyyne, one needs a refined elementary cell with two atoms and, in fact, two lattice constants (see Fig. ). A similar story happens for the tight-binding realization of both chains (discussed in section 3.9) -however -it is applied via the difference of hopping constants, implying that hopping through a single bond is more difficult than hopping through a shorter triple bond.