In the case of cumulene and polyyne molecules, the conjugated 2p carbon electrons effectively form a 1D electron gas. An external charge (q = -0.5e, -1.0e, -1.5e, -2.0e) located 10 Å away from the terminal carbon atom induces charge-density oscillations inside the molecule presented in Fig. . Indeed, in both cases, the Friedel oscillations' decay asymptotics has a 1/r behavior, as expected for the 1D electron gas. Its amplitude linearly depends on the external charge (Fig. ) following the theoretical part of this review (for more details, please refer to the section 1.4.2). On the other hand, for both structures, the corresponding wavelength is strictly related to the C-C distance instead of the Fermi . The insets show the dependence of the strength of charge oscillations (determined by the amplitude of the third positive maximum) on the magnitude of the external point charge. As expected from the linear response theory, the relation is linear and crosses zero in both cases.