New Algorithms and their Use in the Study of Nonadiabatic Processes Influenced by Conical Intersections

新算法及其在受圆锥相交影响的非绝热过程研究中的应用

• 批准号: 1361121
• 负责人: David Yarkony
• 金额: $ 42.5万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1361121&HistoricalAwards=false
• 关键词: New; Algorithms; their; Use; Study

David Yarkony of Johns Hopkins University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to develop theoretical and computational approaches to study chemical reactions that are initiated when a molecule is excited by absorbing energy from light. Scientists can describe a chemical reaction as a marble rolling on a surface: reactants point A; products point B; moving downhill is easy (extract chemical energy); moving uphill is hard (need to add energy). For many light-initiated processes such as photosynthesis, vision, and solar energy conversion, this notion must be generalized. In this case, as the result of absorbing light, the marble starts on a higher surface. Scientists want to know how the marble gets back to the lower surface and where it ends up on that surface, that is, what molecules are made and how much energy they have. If the light is provided by a laser, the task at hand may be laser control of a chemical reaction. If the light comes from the sun, energy conversion, photosynthesis or cell damage may be the issue. The passage from the upper surface to the lower surface not unlike spiraling down a drain - it involves funneling by a double cone-like structure (two cones joined at their vertices) called a "conical intersection". The mathematical description of the resulting multi-surface process requires detailed knowledge of the surfaces and the connecting cones. The more accurate the description of the surfaces and cones the more likely the computer simulation will correspond to reality. The principal goal of this project is the representation of the surfaces and connecting cones using the most accurate tools available and enabling computers to reliably simulate energetic processes. A principal issue in nonadiabatic dynamics is the quality of the electronic structure data (energies and interstate couplings) used. When direct or on-the-fly dynamics techniques are employed, the quality of electronic structure data is subordinated to the need to obtain that data quickly. The alternative is to use fitted coupled potential energy surfaces. This method can use electronic structure descriptions more accurately than those used in direct dynamics and can smooth the irregularities that may occur in the electronic energies due to the orbital changes inherent in nonadiabatic processes. The challenge is to determine the fit. By combining least squares fitting with exact data representation and incorporating derivative coupling data directly into the fitting process, an algorithm has been developed that provides a quantifiably quasi-diabatic fitted representation of electronic structure data including a reliable description of seams of conical intersections. That approach is suitable for 4-5 atom systems. The goal of this research is to extend this algorithm to treat significantly larger molecules, such as the photodissociation of phenol. The proposed fit surfaces algorithm will make high quality electronic structure data available for the study of nonadiabatic dynamics in nucleobases and a multitude of comparably sized systems. Determining how far this methodology can be extended, that is how large a system can be treated, is one of the principal goals of this research.

约翰霍普金斯大学的大卫Yarkony是由化学部的化学理论，模型和计算方法计划的奖项支持，以开发理论和计算方法来研究当分子通过吸收光中的能量而激发时引发的化学反应。 科学家们可以把化学反应描述为在表面上滚动的大理石：反应物点A;产物点B;向下移动很容易（提取化学能）;向上移动很难（需要添加能量）。 对于许多光引发的过程，如光合作用，视觉和太阳能转换，这一概念必须推广。 在这种情况下，由于吸收光，大理石开始在更高的表面上。科学家们想知道大理石是如何回到下表面的，以及它最终在那个表面上的位置，也就是说，什么分子是由它们组成的，它们有多少能量。 如果光是由激光提供的，那么手头的任务可能是激光控制化学反应。 如果光来自太阳，能量转换，光合作用或细胞损伤可能是问题。 从上表面到下表面的通道不像螺旋下降的排水沟-它涉及漏斗由一个双锥状结构（两个圆锥体在其顶点连接）称为“圆锥交叉”。数学描述所产生的多表面过程需要详细的知识的表面和连接锥。 表面和圆锥体的描述越精确，计算机模拟就越有可能符合现实。 该项目的主要目标是使用最精确的工具来表示表面和连接圆锥体，并使计算机能够可靠地模拟能量过程。非绝热动力学的一个主要问题是所用电子结构数据（能量和态间耦合）的质量。当采用直接或动态技术时，电子结构数据的质量从属于快速获得该数据的需要。 另一种方法是使用拟合的耦合势能面。这种方法可以使用电子结构的描述更准确地比直接动力学中使用的，可以平滑的不规则性，可能会出现在电子能量由于固有的轨道变化在非绝热过程。 挑战在于确定合适性。 通过将最小二乘拟合与精确的数据表示相结合，并将导数耦合数据直接纳入拟合过程，已经开发出一种算法，该算法提供了电子结构数据的定量准绝热拟合表示，包括圆锥形交叉点接缝的可靠描述。该方法适用于4-5个原子系统。本研究的目标是将该算法扩展到处理显着较大的分子，如苯酚的光解。建议的拟合表面算法将使高质量的电子结构数据可用于核碱基和众多的非绝热动力学的研究。 确定这种方法可以扩展到什么程度，即可以处理多大的系统，是本研究的主要目标之一。