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深深植根于势能面（PES）的概念。准确计算的能力，不仅是基态，而且激发态PES对于研究大量的化学现象和技术至关重要-飞秒光谱，纳米器件，大气光化学反应和固态化学只是其中的几个例子。在光化学领域的关键重要性是正确描述圆锥形的交叉点，这对应于分子的几何形状，其中两个或多个PES是简并的。锥形交叉点通过充当从分子的激发态到其基态的布居转移的有效漏斗，为光激发分子的非辐射失活提供了超快途径，这是非绝热过程即涉及多于一个PES的过程中普遍存在的现象。 线性响应时间依赖密度泛函理论（LR-TDDFT）是研究分子PES的一种方法。尽管LR-TDDFT取得了很大的成功，但它未能描述基态和第一激发电子态之间的圆锥形交叉点的正确形状和维数。令人惊讶的是，很少有研究是目前在文献中，试图充分考虑LR-TDDFT的维数问题时，描述圆锥相交。仍然有许多明显的问题基本上没有答案。首先，LR-TDDFT在什么情况下能提供圆锥相交的充分描述，什么情况下失效？为什么LR-TDDFT在这种情况下失败，但在其他情况下对圆锥相交给出了足够的近似？一旦对这些问题的答案有了更深入的理解，是否有可能开发一种诊断工具，用于检测LR-TDDFT在准确描述圆锥相交方面的失败？LR-TDDFT中的频率相关核函数能否提供一种可行的方法来改进LR-TDDFT中圆锥相交的描述？为了解决这些问题，拟议的博士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锥形交叉的分子，包括尖峰，倾斜，单路径和/或分叉。在研究中，我们将使用与先进的从头算方法的比较，以获得洞察力，当LR-TDDFT无法再现正确的F-2维数的圆锥相交，以及当它提供了一个足够的描述。有了这个洞察力，我们的下一个目标将是定义一个诊断工具，可以用来确定何时LR-TDDFT/LDA故障，准确地描述圆锥相交。这将是沿着类似的路线，以前的工作由Tozer教授的小组，其重点是诊断测试的发展，以判断性能的密度泛函在其预测的激发能。在标准的电子结构软件包中纳入这样的工具将是至关重要的社区，使用LR-TDDFT在激发态dynamics.Finally模拟，我们建议定期LR-TDDFT计算中的频率依赖性内核的实施进行调查，希望在一个给定的分子中，以促进第一激发态和基态之间的适当耦合。我们计划使用降维模型，其中存在一个数值精确的解决方案，以了解内核在描述两个绝热PES之间的耦合的基本特征。