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Theoretical Investigations on Transition Voltage Spektroscopy (TVS)

过渡电压谱 (TVS) 的理论研究

基本信息

批准号：
230940220
负责人：
Dr. Ioan Baldea
金额：
--
依托单位：
Forschungsgruppe Theoretische Chemie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2015-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/230940220?language=en
关键词：
Theoretical Investigations Transition Voltage Spektroscopy

项目摘要

The project is devoted to the theoretical investigation of the Transition Voltage Spectroscopy (TVS). TVS is an experimental tool of molecular electronics proposed recently by Frisbie et al, which aims at determining the relative energetic alignment of the molecular orbitals with respect to metal's Fermi level from the (transition) voltage at the minimum of the Fowler-Nordheim (FN) diagram. The FN diagrams are directly obtained from the measured I-V curves. The orbital energy offset is a key parameter for molecular transport, because it controls the charge transfer efficiency. In close collaboration with two experimental groups, the work planned in this project will attempt to provide a firm theoretical foundation of TVS. To this aim, an approach of molecular transport based on molecular orbitals with a clear physical meaning (as opposed to Kohn-Sham orbitals) is needed. The main methodological goal of this project is to develop and implement an ab initio (not based on Density functional theory (DFT)) approach to molecular transport relying upon the outer valence Green's functions (OVGF), a well-established method of quantum chemistry. It is backed by four decades of work in quantum chemistry, demonstrating that the outer valence region can be accurately described within a single-particle picture. Such an ab initio transport approach based on dressed quasi-particles that incorporate post-HF (Hartree-Fock) electron-electron interaction effects is not only of interest for TVS but also for the molecular transport theory in general. In implementing the OVGF-based transport approach, the computational advantage offered by the Cholesky decomposition will be exploited, which enables calculations for large molecules with high-quality basis sets and reasonable computing cost. The basic TVS idea was to provide experimentalists with a simple tool to directly determine the orbital energy offset without the need to resort to sophisticated transport calculations. This practical goal, at which the project also aims, can be achieved only if sufficiently simple models can be utilized, whose parameters can be extracted from experimental data and validated by microscopic calculations. Realistic models will be proposed that will extend the Newns-Anderson model, which has been employed in recent studies and turned out to successfully explain a series of experimental TVS findings. Extensions envisaged in this project will incorporate, e. g., the effect of anchoring groups and electrodes' work function, whose significant impact on the transition voltage has been demonstrated in recent experimental studies. The impact of stochastic fluctuations on two-dimensional transition-voltage-conductance histograms (that became available due to recent experimental achievements of Tao et al) and of the inner reorganization on TVS for molecules with a floppy degree of freedom will also constitute important topics of investigation.

本项目致力于过渡电压谱(TVS)的理论研究。TVS是Frisbie等人最近提出的一种分子电子学实验工具，其目的是从Fowler-Nordheim(FN)图的最小跃迁电压确定分子轨道相对于金属费米能级的相对能量排列。由测得的I-V曲线直接得到Fn图。轨道能量偏移量是分子输运的关键参数，因为它控制着电荷转移效率。与两个实验小组密切合作，本项目计划的工作将试图为电视节目提供坚实的理论基础。为此，需要一种基于具有明确物理意义的分子轨道(而不是Kohn-Sham轨道)的分子传输方法。这个项目的主要方法论目标是发展和实现一个从头算(不是基于密度泛函理论(DFT))依赖于外价格林函数(OVGF)的分子输运方法，OVGF是一种成熟的量子化学方法。它得到了40年来量子化学工作的支持，证明了可以在单粒子图像中准确地描述外部价区。这种基于包含后HF(Hartree-Fock)电子-电子相互作用效应的修饰准粒子的从头算输运方法不仅对TVS感兴趣，而且对一般的分子输运理论也是感兴趣的。在实现基于OVGF的输运方法时，将利用Cholesky分解提供的计算优势，使大分子的计算具有高质量的基组和合理的计算成本。TVS的基本想法是为实验者提供一种简单的工具来直接确定轨道能量偏移量，而不需要求助于复杂的运输计算。只有利用足够简单的模型才能实现这一实际目标，这也是该项目的目标，这些模型的参数可以从实验数据中提取并通过微观计算进行验证。将提出现实的模型，以扩展纽斯-安德森模型，该模型已被用于最近的研究，并被证明成功地解释了一系列电视实验结果。本项目设想的扩展将包括，例如，锚定基团和电极的功函数的影响，它们对转变电压的显著影响已在最近的实验研究中得到证实。随机涨落对二维跃迁-电压-电导直方图的影响(由于陶渊明等人最近的实验成果而成为可能)，以及分子的内部重组对具有松弛自由度的分子的电导的影响也将成为重要的研究课题。