中文摘要：

在第一性原理基础上，理论研究了苯环上含有不同取代物的四个联苯分子的电输运特性．计算结果表明，当苯环上的氢被取代时，联苯分子的两个苯环之间的扭转角增大．分子结的电导随苯环间扭转角的增加而减少，且电导值与扭转角余弦平方成线性关系．在低偏压下，分子结的电输运机制是电子通过Ⅱ轨道的隧穿过程．计算结果与实验结果符合的较好．

英文摘要：

The electronic transporting properties of biphenyl molecules with different ring substitutions are studies at the first-principles level. The results show that the twist angle θ between the two benzene rings increases as the hydrogen atoms in the ring are substituted. Consequently, the junction conductance decreases as the θ increases. Furthermore, it demonstrates that the junction conductance has a linear relation with cos2θ , which indicates that the tunneling transport through the π-orbitals plays a domi- nant role for the junction conductance at low bias. The simulation results are relatively consistent with the measurement.