中文摘要：

该文用第一性原理非平衡格林函数方法研究了团簇与电极之间的距离和门电压对团簇Al4输运性质的影响.团簇Al4放置在两个半无限长的Al（100）电极中.研究结果发现：体系平衡电导随电极距离的增大并不是单调变化,而是先增大,后减小;随着门电压变化,平衡电导呈现出振荡行为,且团簇与电极之间的距离对其平衡电导的振荡特性有很大的影响.当接触距离固定时,团簇Al4体系的导电率随着门电压变化出现高电导态和低电导态,表现出一种分子开关行为.通过分析各种情况下体系费米能级处的总态密度（DOS）,我们发现系统的平衡电导的变化来源于费米能级处态密度的变化.如门电压引起的电导振荡行为是由于在门电压的作用下,Al4团簇的能级发生移动使得团簇的能级和电极的费米能级连接发生变化,从而导致系统在费米能级处的总态密度的变化.电荷转移分析显示：无论是改变团簇电极间的距离,还是改变门电压,电荷转移都不是平衡电导变化的主要因素.

英文摘要：

We investigate the effects of the separation distance between the electrodes and the central molecule and gate-voltage on the transport properties of cluster Al4 coupled to two Al（100） electrodes based on a recently developed ab initio non-equilibrium Green function method.The following are the results.The equilibrium conductance doesn＇t change monotonously with the increase of the distance,but increases firstly and then decreases.The gate-voltage affects the equilibrium conductance in an oscillatory manner,and this manner is influenced greatly by the distance.And at a fixed distance,there exists high conductivity and low conductivity with the variation of gate-voltage,which demonstrates a field-induced molecular switch behavior.Under the analysis of DOS at the Fermi level for all the cases,we find that reason for variation of the equilibrium conductance is the variation of the DOS at the Fermi level.The charge transfer calculation analysis shows that the conductances for all the cases have nothing with the charge transfer.