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In this thesis,based on the DFT+NEGF first-principles method,we construct a lead-molecule-lead sandwich system with single benzene-based molecule to investigate the relationship between the structure and properties of the molecular devices and the factors that influence properties of the molecular devices.Our computational investigations on these molecular devices are primarily concentrated on the effect of contact geometry between molecules and electrodes,the effect of side groups,the effect of different torsion angle between two phenyl rings and the effect of external electric field.This thesis consists of five chapters:In Chapter one,we mainly introduce the research background and development of the molecular electronics,including the experimental fabrication of molecular electronic components and theoretical simulation methods.Afterwards we discuss the questions that need to be solved in this area.Finally,the main contents of this thesis are listed.In Chapter two,we introduce the theoretical methods used in this thesis, including the main first-principles calculation methods,i.e.,the Density-Functionmethod and nonequilibrium Green\'s function.

本论文拟采用密度泛函理论和非平衡格林函数相结合的第一性原理计算方法，选取苯基小分子作为研究对象，构建了金属电极/有机小分子/金属电极三明治结构体系，系统地研究了苯基分子器件结构的改变与分子电输运性质之间的关系以及影响分子器件电输运性质的相关因素，其中重点研究了分子与电极间可能的接触结构改变、官能团、分子间的扭转角以及外电场对苯基分子电输运性质的影响，本论文主要包括以下五个章节的内容：第一章为综述部分，主要介绍了分子电子学产生的背景、分子器件的研究意义、当前研究分子器件的实验和主要理论方法，以及目前在研究分子器件中存在的一些问题，最后给出了本论文的主要研究内容和技术路线。

The process of the removal of a apolar molecule or the hydrophobic moieties from water can be considered as two steps: One is the destructuring of the water in the vicinity of the surface of the solute molecules, and the other is the cavity holding the hydrocarbon molecule collapses.

非极性分子或极性分子的疏水部分从水中逸出的过程可视为由两部分组成：一是非极性分子周围的水分子的有序排列结构被破坏；二是水中容纳非极性分子的空穴倒坍。

The influences of the inclusion of Na~+ into each conformer (C7AB, C7"AB, C7eqB, C5A, C7axB orα"B) of AD molecule on the Ramachandran angles of molecular backbone and the hydrogen bonds in AD moiety were discussed in detail. It was found that in the forming process of bidentate structures of Na~+-AD ion-complexes, the original H-bonds in AD molecule were fully broken down, accompanying with the new formation of the two Na-O bonds.

论文中详细探讨了Na~+-AD络合离子六种构象的空间构型，分析了丙氨酸二肽与Na~+作用过程中AD分子骨架Ramachandran角及分子内N(1)–H(1)…O(2)、N(2)–H(2)…O(1)、N(1)–H(1)…N(2)和N(2)–H(2)…N(1)氢键的变化，研究发现Na~+与AD分子形成双齿结构时，AD骨架中原先的氢键全部被破坏，继而形成了两个新的Na-O键；Na~+与AD分子形成单齿络合离子时，AD骨架中原先的氢键或者得到增强或者断裂之后出现新的强度更大的氢键。

A universal analytic potential energy function is derived using the cosine function with a phase factor,which is suitable to be applied to the interactions between two atoms in a molecule or molecule and ion.5 kinds of common potential curves are obtained by adjusting phase factors.

利用一种带相位因子的余弦函数，导出了适用于双原子分子或分子离子间相互作用的普适性解析势能函数，通过调节相位因子可获得5种常见形态的势能曲线。

Introduction】Enriched with several kinds of plants protein, particularly the Dextrorotation high protein molecule and the high protein molecule and high anti-oxidant substance-Q22 owned by the berries, balance the value of the PH of the hair, makes the hair shiny and vibrant, and moisture lost, no stimulus, leaves the hair shiny and elegant.

含有北极多种植物蛋白及浆果特有的左璇高蛋白分子及高纯度抗氧化物-Q22：平衡毛发之ph值使头发恢复光泽弹性，修复受损发质，防止头发干枯、僵硬、打结、起静电及水分流失，温和不刺激，使用后清新爽洁，闪烁动人，让秀发更飘逸。

The ground state of C2 molecule is studied using VB mehods. The potential energy curves of the C2 diatomic molecule were computed by using ab initio VB methods, VBSCF, BOVB, and VBCI. The computational results show that the VB-based PECs are parallel to that of Full CI calculation.

应用XMVB程序对C2分子的基态进行了理论研究，计算结果表明价键方法能够给出和FCI相平行的解离势能曲线；高级别的VB方法，VBCISD方法，能够得到和高等级分子轨道方法相符的解离能。

Using the method we calculate the 〓 elasticdifferential scattering cross section, excitation differential scattering crosssection, and excitation cross section of electron collision with 〓 We transform the electron and molecule problem into electron problemby Born-Oppenheimer approximate. Mr Rossi, Dr. the Flinders University ofSouth Australia, calculated electron collision with molecule, but theexchange term he used become bigger and bigger as incident energyincreases, it is unreasonable, besides, the potential of electron and nucleus heused is somewhat rough. At present we correct these two terms. The potentialconsists of static potential, exchange potential, polarization potential.

电子与分子的碰撞过程的相互作用势主要是由静态势、交换势和极化势三部分决定的，这里对这三部分在动量空间中进行分波展开，推导出易于计算的表达形式，根据这些公式，并参考Rossi的弹性碰撞程序编写了计算电子与分子碰撞激发截面的程序，利用程序计算出势能矩阵元，通过求解Lippmann-Schwinger方程求得T矩阵元，便可求得散射截面。

It was found that the process of the dimerization of ethene can be divided into three steps: the chemical adsorption of first ethene molecule, the physical adsorption of second ethene molecule and the dimerization reaction.

研究表明，乙烯在分子筛上的二聚反应分三步进行：单个乙烯分子化学吸附→第二个乙烯分子的物理吸附→两乙烯分子二聚反应。

Sucrose, table sugar, is a disaccharide composed of one molecule of glucose and one molecule of fructose.

蔗糖，白砂糖是由一个葡萄糖分子和一个果糖分子组成的二糖。

It may result from the coupling of acarbonyl group in one molecule with the double bond in another molecule.

它是由一分子环丁烯二酮的羰基碳与另一分子的双键β-碳发生还原偶联的结果。

Lugalbanda was a god and shepherd king of Uruk where he was worshipped for over a thousand years.

Lugalbanda 是神和被崇拜了一千年多 Uruk古埃及喜克索王朝国王。

I am coming just now,' and went on perfuming himself with Hunut, then he came and sat.

我来只是现在，'歼灭战perfuming自己与胡努特，那麼，他来到和SAT 。