中文摘要：

基于杂化密度泛函理论,研究了1,4-丁二硫醇分子体系的结构随电极作用力的变化及拉断过程；并利用弹性散射格林函数方法进一步计算了不同电极作用力下分子体系的电输运特性.结果显示,界面结构不同,拉断分子体系所用的拉力也不同：分子末端硫原子处于Au（111）面的空位上方时,拉断分子体系需约1.75 nN的拉力；若金电极表面存在孤立金原子与1,4-丁二硫醇分子末端的硫原子相连,拉断分子体系只需约1.0 nN的力,且伴有孤立金原子被拉出.两种情况分别与不同实验测量相符合.分子在压缩过程中发生扭曲并引起表面金原子滑移,然而压缩扭曲过程与拉伸回复过程不可逆.电极拉力约为0.7-0.8 nN时,分子体系在不同界面构型下以及在不同扭转状态下,电导都出现极小值,这与实验结论一致.分子的末端原子与电极间耦合强度随电极作用力的变化是引起分子体系电导变化的主要因素.实验在0.8 nN附近同时测得较小概率的高电导值与双分子导电有关.

英文摘要：

Based on the hybrid density functional theory, the relationship between geometric structure of 1,4-butanedithiol molecular junction and the electrodes force and the breaking process of the molecular junction are studied. The electronic transport properties of the molecular junction under different external forces are further investigated using the elastic scattering Green’s function method. The numerical results show that different interface configurations result in different rupture forces. The rupture force is about 1.75 nN when the terminal S atom is sited at the hollow position of Au（111） surface. However, the rupture force is about 1.0 nN when the terminal S atom links with one Au atom which is on the gold surface singly. And with the breakdown of the molecular junction, the single Au atom is pulled away from the gold surface by the terminal S atom. These two results are consistent with different experimental measurements respectively. The molecule is twisted under the electrode pressure and thus further induces the surface Au atom to glide on the gold surface. However, the processes of the molecule twisted by pressure and restored by pulling are two irreversible processes. The stretching force of electrode is 0.7-0.8 nN, and the conductance always shows a minimal value under different interface configurations and twisting states, which is consistent with experimental conclusion. The change of the coupling between the terminal atom and the electrodes induced by the electrode force is the main factor of influencing the conductance of the molecular system. The existence of bimolecular junction results in a small possibility of higher conductance values, which is probed by experiment under a stretching force of about 0.8 nN.