Conical intersections within linear-response time-dependent density functional theory

线性响应时间相关密度泛函理论中的圆锥相交

• 批准号: 2571940
• 金额: --
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2571940
• 关键词: Conical; intersections; within; linear; response

Our understanding of chemical reactions is heavily rooted in the concept of potential energy surfaces (PESs). The ability to accurately compute, not only ground state, but also excited state PESs is crucial for the study of a vast array of chemical phenomena and technologies - femtosecond spectroscopy, nanoscale devices, atmospheric photochemical reactions and solid state chemistry are just a few examples of these. Of key importance in the field of photochemistry is the correct description of conical intersections, which correspond to molecular geometries at which two or more PESs are degenerate. Conical intersections provide an ultrafast route for nonradiative deactivation of photoexcited molecules by acting as efficient funnels for population transfer from a molecule's excited states to its ground state, a phenomenon that is ubiquitous to non-adiabatic processes i.e. those involving more than one PES. One method of choice for the study the PESs of a molecule is linear-response time-dependent density functional theory (LR-TDDFT). Despite all its successes, LR-TDDFT fails to describe the proper shape and dimensionality of conical intersections between the ground and the first excited electronic state. Surprisingly, little research is present in the literature that attempts to fully characterise LR-TDDFT's dimensionality problem when describing conical intersections. There are still many obvious questions that remain largely unanswered. Firstly, when does LR-TDDFT provide an adequate description of conical intersections and when does it fail? Why does LR-TDDFT fail in such cases, but give a sufficient approximation to conical intersections in others? Once a deeper understanding of the answers to these questions has been found, is it possible to develop a diagnostic tool that can be used to detect LR-TDDFT's failure in accurately describing conical intersections? Could frequency-dependent kernels in LR-TDDFT provide a viable way of improving the description of conical intersections within LR-TDDFT? To address these questions, the proposed PhD project will be split into the following three main parts:Firstly, we propose to study a series of molecules exhibiting different types of conical intersection, including peaked, sloped, single-path and/or bifurcating. Within the investigation, we will use comparisons with sophisticated ab initio methods to gain insight into when exactly LR-TDDFT fails to reproduce the correct F-2 dimensionality of conical intersections, as well as when it provides a sufficient description.With this insight, our next aim will be to define a diagnostic tool that can be used to determine when LR-TDDFT/LDA breaks down in accurately describing conical intersections. This will be along similar lines to previous work by the group of Prof. Tozer, which focused on the development of a diagnostic test to judge the performance of density functionals in their prediction of excitation energies. Incorporation of such a tool in standard electronic structure packages would be vital for the community that use LR-TDDFT in the simulation of excited state dynamics.Finally, we propose to investigate the implementation of a frequency-dependent kernel in regular LR-TDDFT calculations, in the hope to facilitate proper coupling between the first excited and ground states in a given molecule. We plan to use reduced dimensionality models, for which a numerically-exact solution exists, to understand the underlying features of the kernel in describing the coupling between the two adiabatic PESs.

我们对化学反应的理解很大程度上根植于势能表面（PESS）的概念。准确计算的能力不仅基态，而且激发的状态佩斯对于研究各种化学现象和技术的研究至关重要 - 飞秒光谱，纳米级设备，大气光化学反应和固态化学反应和固态化学只是几个例子这些。光化学领域的关键重要性是对锥形交叉点的正确描述，这与分子几何相对应，在该几何形状上，两个或多个佩斯是退化的。圆锥形交集通过充当从分子激发态到其基态的有效人口转移的有效人口转移，这为光激发分子的非辐射式停用提供了超快速途径，这种现象是无处不在的非启发过程。 研究的一种选择方法是分子的PESS是线性响应时间依赖性密度功能理论（LR-TDDFT）。尽管取得了所有成功，但LR-TDDFT仍未描述地面与第一个激发电子状态之间圆锥形相交的正确形状和维度。令人惊讶的是，文献中很少有研究在描述圆锥形交叉点时试图完全表征LR-TDDFT的维度问题。仍然有许多明显的问题在很大程度上尚未得到答复。首先，LR-TDDFT何时提供对圆锥形交集的足够描述，什么时候失败？在这种情况下，为什么LR-TDDFT失败了，而是对其他人的圆锥形交集给出足够的近似值？一旦发现了这些问题的答案，是否有可能开发可用于检测LR-TDDFT在准确描述圆锥形相交时的失败的诊断工具？ LR-TDDFT中的频率依赖性内核是否可以提供一种可行的方法来改善LR-TDDFT内锥形相交的描述？为了解决这些问题，拟议的博士学位项目将分为以下三个主要部分：首先，我们建议研究一系列表现出不同类型的圆锥形交集的分子，包括峰，倾斜，单路和/或分叉。在调查中，我们将使用与先进的摘要方法的比较来深入了解何时何时LR-TDDFT无法重现圆锥形交集的正确F-2维度，以及何时提供足够的描述。下一个目的是定义一个诊断工具，该工具可用于确定何时在准确描述圆锥形交叉点时分解LR-TDDFT/LDA。这将与Tozer教授小组的先前工作相似，该研究的重点是开发诊断测试，以判断其在激发能量的预测中的密度功能的性能。将这种工具纳入标准电子结构包中对于在激发态动力学模拟中使用LR-TDDFT的社区至关重要。在本文中，我们建议研究在常规的LR-TDDFT计算中实现频率依赖性内核的实施，希望在给定分子中促进在第一个激发和基态之间进行适当的耦合。我们计划使用降低的维数模型，其中存在数值脱颖而出的解决方案，以了解内核的基本特征，以描述两种绝热佩斯之间的耦合。