As mentioned previously, FOs are most pronounced in the case of one-dimensional quantum systems (please see Fig. ). In fact, the FOs observed for the one-dimensional Dirac-Kronig-Penney crystal model (for more details please see section 3.6), could also manifest in existing conjugated long-chain molecules. Good examples of the molecules that satisfy this condition are cumulene and polyyne carbon chains, having all-double and alternating single-triple bonds, respectively. Given sufficient chain length, those two molecules could be treated as approximations to the ideal crystal case, presented in section 3.5, and can be described theoretically either within a tight-binding framework or as a Dirac-Kronig-Penney crystal (section 3.6). Cumulenes and polyynes also satisfy another important condition -they are wellstudied systems from both experimental (synthesis) and theoretical perspectives. This makes them the perfect candidates to compare the physical phenomenon of FOs against chemical knowledge. In this section, we analyze oscillations based on electron densities since the latter are consistent with the theoretical part and are basis set independent, thus allowing us to make reliable conclusions.