Center for Atomic-scale Materials Design (CAMD), Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
J Chem Phys. 2011 Oct 14;135(14):144104. doi: 10.1063/1.3646510.
The conductance of a molecular wire connected to metallic electrodes is known to be sensitive to the atomic structure of the molecule-metal contact. This contact is to a large extent determined by the anchoring group linking the molecular wire to the metal. It has been found experimentally that a dumbbell construction with C(60) molecules acting as anchors yields more well-defined conductances as compared to the widely used thiol anchoring groups. Here, we use density functional theory to investigate the electronic properties of this dumbbell construction. The conductance is found to be stable against variations in the detailed bonding geometry and in good agreement with the experimental value of G=3×10(-4) G(0). Electron tunneling across the molecular bridge occurs via the lowest unoccupied orbitals of C(60) which are pinned close to the Fermi energy due to partial charge transfer. Our findings support the original motivation to achieve conductance values more stable towards changes in the structure of the molecule-metal contact leading to larger reproducibility in experiments.
与金属电极相连的分子导线的电导已知对分子-金属接触的原子结构敏感。这种接触在很大程度上取决于将分子导线与金属连接的锚定基团。实验已经发现，与广泛使用的硫醇锚定基团相比，作为锚定基团的 C(60)分子的哑铃结构产生了更明确的电导。在这里，我们使用密度泛函理论研究了这种哑铃结构的电子特性。发现电导对详细键合几何形状的变化稳定，并且与实验值 G=3×10(-4) G(0)非常吻合。分子桥的电子隧穿通过 C(60)的最低未占据轨道发生，由于部分电荷转移，这些轨道被固定在费米能级附近。我们的发现支持了实现对分子-金属接触结构变化更稳定的电导值的原始动机，从而导致实验中更大的重现性。
