端基对分子器件整流性质的影响

利用基于非平衡Green函数加密度泛函理论的第一原理方法，研究了以S(Se)为端基的三并苯环分子夹在两半无限长的Au电极之间构成双探针系统的输运特性，发现体系具有较好的整流效应，最大整流系数达到6；用H取代右端同一位置的一个S（Se），整流行为明显减弱.分析认为，这种整流是由于分子两端与电极的耦合不对称，使正负偏压下分子能级的移动和空间轨道分布不同所致.比较而言，S端基与电极的耦合导致的整流比Se强.关键词：电子输运整流行为非平衡Green函数方法

Effects of end groups on the rectifying performance in molecular devices

Based on the density-functional theory and the non-equilibrium Green's function method,a theoretical study of the electron transport for the systems consisting of the terphenyl molecule connected to two Au electrodes through end-group S (Se)is carried out.The results show that these systems have good rectifying performance and the maximum rectification ratio may reach approximately 6 at a bias of 2.8 V.The rectifying behavior is reduced significantly when one of the two S (Se)atoms located at right end of the molecule is replaced by H.The asymmetric coupling between the molecule and the metal interface leads to different spatial distributions of the MPSH and different shifts of molecular orbital energy levels under positive and flegative biases,which is the mechanism of rectifying performance.The systems with S end-groups have obvious rectifying performance because the interaction between S and Au electrode is stronger than that between Se and Au electrode.