Moreover, the Fermi wavevector kF fit is independent of the point charge size (as it is characteristic of the system itself) and is equal to 1.23 1/Å and 1.21 1/Å for cumulene and polyyne, respectively. These are related to the average bond length ⟨|C-C|⟩ for cumulene (1.275 Å) and polyyne (1.292 Å). The formula relating these two quantities is