Friedel oscillations appear in systems characterized by delocalized electron structure. Thus, they could also be present in any molecule with conjugated bonds. Canuto et al. have shown a similarity in charge density oscillation on metal surfaces and a well-known phenomenon of atom-wise alternating charges (i.e., alternating polarity) in polyene chains for both unperturbed and perturbed cases. They have presented the charge-density oscillations for both unperturbed and perturbed cases. The oscillatory pattern in polyenes appears already at the Hückel theory level as well as at free electron level approximation, thus revealing the origin of the oscillations to be atom-atom polarizabilities. In fact, such charge distribution is to be expected from experimental chemistry, given the varying reactivity for the different atomic positions along the chain. Interestingly, the charge oscillation of the non-neutral chain does not follow the expected atom-wise character and depends on the electron density instead -meaning that for a chain with M sites and N free electrons, the period of oscillations becomes equal to λ = 2M a/N = a/r, where a is lattice constant. Our calculations on the unperturbed chain also show clear oscillations caused by the termini -acting as perturbations (Fig. ). The perturbation is highly localized on both ends of the polyene chain, decaying towards the center. The presence of the terminus-induced FOs in half-filled-band structures (such as polyene, cumulene, and polyyne) shows that a simple tightbinding model alone is not enough to describe precisely the electronic structure of open carbon chains. Here, for the filling factor r = 0.5 (half-filled band), tight-binding predicts no charge density oscillations. However, oscillations readily appear for other filling factors. For example, the pattern shown as a dashed line in Fig. ) has been obtained with r = 10/16, meaning a total of 10 free electrons in C16 carbon chain. This number has been chosen as the closest to 0.5 ≡ 8/16, which also preserves the mirror symmetry, requiring an even number of electrons and has maxima placed at the chain ends. However, such FOs case is nicely reproduced if the π-electron system is treated more like the free electron gas, which has also been shown by Canuto et al.