Electronic structure theory: Approximations to the exchange-correlation energy and models for electron transport

电子结构理论为我们理解化学、生物化学、材料科学、凝聚态物质等提供了基础。它还提供了在上述各个领域进行计算建模的工具。提出的研究旨在推进电子结构理论的几个领域。其中一个重点将是密度泛函理论（DFT），其中我们将讨论电子之间的交换相关能。这是Kohn-Sham DFT的关键组成部分，它解释了电子之间复杂的相互作用。在这一领域取得了巨大的进步，使Kohn-Sham DFT成为化学中使用最多的工具，也是物理科学史上被引用最多的话题。然而，仍然有许多系统和性质，现有的近似是不可靠的。在前人工作的基础上，我们的研究计划旨在加深我们对交换相关能的理解，并改进现有的交换相关函数。这将提供更好的计算工具，进一步简化所有科学技术领域新材料和化合物的设计。此外，我们打算继续我们在分子电子学领域的工作，其中分子连接到触点，并且通过分子的电流作为施加电压的函数进行测量。在过去，我们为分子电子器件开发了简单的模型，使我们能够预测新的现象，其中一些已经被实验证实。在提出的研究中，我们希望改进和扩展我们的理论。例如，我们希望为相干分子光伏电池开发简单的基于h<s:1>克尔的模型以及复杂的基于dft的模型。在这些装置中，电子能量通过光子的吸收在分子中穿行而增加。整个收集光子能量的机制是相干的，这意味着这个过程可以用一个波函数来描述，这个波函数是一个特征值方程的平稳解。这种相干机制将分子光伏电池与传统光伏电池区分开来。分子光伏电池可能会更有效地将太阳光转化为电能，通过我们的研究，我们探索了这种装置的可行性，并为其实现提供指导。

Electronic structure theory provides the basis for our understanding of much of chemistry, biochemistry, material science, condensed matter etc. It also provides the tools for computational modeling in the various areas mentioned. The proposed research aims at advancing several fields of electronic structure theory. One focus will be on density functional theory (DFT), where we address the exchange-correlation energy among electrons. This is the crucial component of Kohn-Sham DFT and it accounts for the complicated interactions between electrons. There has been enormous progress in this area which made Kohn-Sham DFT the most used tool in chemistry and the most cited topic in the history of the physical sciences. However, there remain numerous systems and properties for which the existing approximations are not reliable. Building on and continuing our previous work, our research program aims at deepening our understanding of the exchange-correlation energy and at improving upon existing exchange-correlation functionals. This will provide better computational tools, further simplifying the design of new materials and compounds in all areas of science and technology. ***Furthermore, we intend to continue our work in the area of molecular electronics where molecules are connected to contacts and the current that passes through the molecule is measured as a function of the applied voltage. In the past we developed simple models for molecular electronic devices that enabled us to predict new phenomena some of which have been verified experimentally. In the proposed research we want to improve and extend our theories. For example, we want to develop simple Hückel-based as well as sophisticated DFT-based models for coherent molecular photovoltaic cells. In these devices, the electron energy is increased upon traversing the molecule through the absorption of a photon. The entire mechanism of harvesting the photon energy is coherent, meaning that the process can be described by a single wave function that is a stationary solution of an eigenvalue equation. This coherent mechanism distinguishes molecular photovoltaic cells from conventional photovoltaic cells. Molecular photovoltaic cells might turn out to be more efficient to convert the energy of sunlight into electrical energy and with our research we explore the feasibility of such devices and provide guidance for their realization.