First Principles Studies of the Structural Evolution of a Dicyanobenzene Molecular Junction with Gold Electrodes

Molecular electronics have attracted attention due to their potential in decreasing the size of transistors to the molecular scale. We present our first principles studies of the structural and electronic properties of a single-molecule dicyanobenzene junction with gold electrodes. Density functional theory (DFT) was used to simulate the formation process of the dicyanobenzene molecular junction by elongating a gold nanowire with a dicyanobenzene molecule placed above a thin gold wire. As the wire was stretched and broken, we found four significant stages of system rearrangement. The molecule first rotated (the first stage) and then gradually slipped into the junction and bonded to the gold atomic tips in three stages. For each stage, we performed calculations using the non-equilibrium Green’s function combined with the DFT (NEGF-DFT) method to obtain the electronic transport pathway and the conductance of the molecular junction. We found that after the main transmission channel switches from via the gold bridge to via the molecule, the conductance increases while the junction is elongated, which is due to an interesting alignment between the frontier molecular levels and the Fermi energy of the electrodes.