Zero Bias Electron Transport Properties of Molecular Junctions Formed from Smallest Fullerenes C20 and C24

Using density functional theory and the non-equilibrium Greens function formalism, we compare the zero bias electronic properties of two molecular junctions formed from the smallest fullerenes: C20 and C24. The results show that both junctions exhibit superconducting properties of the order of 2.5G0 and 3.12G0, respectively. The C24 junction exhibits a smaller HOMO-LUMO gap and higher zero bias conductance. The electronic wave functions are examined to understand the origin of the transmission peaks and resulting conductance. We find that for the C24 junction, the electrodes donate charge to the molecule giving rise to an occupied and unoccupied state very close to the Fermi level, resulting in a high and broad transmission peak that is responsible for the high conductance. For the C20 junction, the molecule loses some electron density and transmission is via unoccupied orbitals close to the Fermi level.