分子尺度结构的量子和经典动力学
Quantum and Classical Dynamics of Molecular Scale Structures
摘要：
在这篇论文中，我研究了由单分子形成的分子结的分子电子性质。本文首先讨论了本论文所采用的主要理论方法：密度泛函理论和电子输运的格林函数方法。这两种技术在第四章中被用来研究二羧酸封端的烷烃与石墨烯金纳米间隙电极的电荷输运。然后将结果与使用对称金电极的结果进行了比较，并揭示了由于费米能相对于分子前线轨道的差异，两种情况之间存在差异。此外，非对称结中的电导率高于对称结中的电导率，这表明石墨烯在利用羧酸锚定基团时提供优异的电极性能。第五章研究了链上引入氧对饱和链电导的影响。对低聚醚链的电子结构计算结果与前人对烷烃的电子结构计算结果的比较表明，低聚醚的电导率低于相同长度烷烃的电导率。我发现烷烃的每个甲基单元的β隧穿因子低于低聚醚的β因子。在最后一章中，分子动力学模拟被用来检查石墨烯基分子电子学的两个候选分子的分子组装，一个与一个芘锚，芘PEGn exTTF，PPT，和其他与三个芘锚，三芘衍生物，TPPT，在无序石墨烯表面上。PPT被视为形成平坦结构，而TPPT被视为在石墨烯表面上形成半圆锥形胶束结构。在水的存在下，PPT倾向于聚集，而TPPT胶束膨胀。
英文摘要：
In this thesis, I investigate the molecular electronic properties of molecular junctions formed from single molecules. I started my thesis by discusses the main theoretical methods using in this work density functional theory and the green function formalism of electron transport. These two techniques are used to study the charge transport through dicarboxylic acid terminated alkanes in chapter 4, with graphene gold nanogap electrodes. The results are then compared with those using symmetric gold electrodes and reveal that there is a difference between the two situations due to the difference in Fermi energies relative to the frontier orbitals of the molecules. Furthermore, the electrical conductance in the asymmetric junction is higher than that in the symmetric junction, which suggests that graphene offers superior electrode performance when utilizing carboxylic acid anchor groups. In chapter 5, I study affected of the saturated chain conductance by adding oxygen to the chain. Comparisons between my electronic structure calculations on oligoether chains and previous work on alkanes show that the conductance of oligoether is lower than that of alkane chains with the same length. I found that the beta tunneling factor per methyl unit of the alkanes is lower than the beta factor of oligoether. In the final chapter, molecular dynamic simulations are used to examine the molecular assembly of two candidate molecules for graphene-based molecular electronics, one with one pyrene anchor, Pyrene PEGn exTTF, PPT, and the other with three pyrene anchors, tri pyrene derivative, TPPT, on a disordered graphene surface. PPT is seen to form flat structures whilst TPPT is seen to form semicircular cone like micelle structures on the graphene surface. In the presence of water, the PPT tends to aggregate whereas the TPPT micelle expands.
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