Understanding excited-state properties of molecules in solution using embedded, accurate ab-initio wave functions

使用嵌入式、精确的从头算波函数了解溶液中分子的激发态特性

• 批准号: 253455322
• 负责人: Privatdozent Dr. Sebastian Höfener
• 金额: --
• 依托单位: Abteilung für Theoretische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/253455322?language=en
• 关键词: Understanding; excited; state; properties; molecules

The adequate description of solvation phenomena is the key to successful computational modeling of molecular properties in solution.The project aims at understanding excited-state properties of molecules in complex environments by dividing the system into subsystems and using ab-initio wave-function methods.When investigating a molecular complex in a non-trivial environment with ab-initio quantum chemistry, one faces different challenges at the same time. An obvious problem is the steep scaling of the available (wave-function) methods so that in practice only a very limited number of atoms can be treated. A more subtle problem with increasing system size is the amount of states and degrees of freedom arising due to the number of molecules involved, so that, independently of the method used, an explicit treatment of all molecules in a supermolecular calculation makes the analysis of chemically motivated subunits often too hard.One useful ansatz is given by embedding methods, which divide the supersystem into smaller subunits, so that a very limited number of states are left which are by definition assigned to a certain molecule, and the scaling problem is significantly reduced. Frozen-density embedding (FDE) has proven to be an efficient approach to divide a complex consisting of several molecules, with all subsystems treated using ab-initio methods. One of the main features of this method is to allow for a systematic, consistent and rigorous derivation for the most common molecular properties with wave-function methods, avoiding special-case treatments for some properties, or the need to reparameterize semi-empirical parameters.In this project, we shall develop analytical nuclear gradients for an approximated coupled-cluster singles and doubles (RI-CC2) FDE for both ground and excited states. The new method can be used to investigate the origin of excitations and their influence on the (excited-state) geometry in complexes with solvation shells, while it is possible to discriminate between significantly shifted local excitations and ''true'' super-system effects, such as inter-fragment charge-transfer excitations. The main applications of this project are seen in small molecular complexes surrounded by explicit solvation molecules for which the RI-CC2 method is applicable. This yields a large variety of interesting complexes, ranging from for instance deoxyribonucleic acid (DNA) dimers to the benzene dimer, i.e. from hydrogen bonds to van-der Waals interactions. Particularly, systems of interest are excimers in solution, where an excited-state geometry optimization is significantly more efficient than a single-point scan if more than one degree of freedom needs to be taken into account.

对溶剂化现象的充分描述是成功模拟溶液中分子性质的关键。本项目旨在通过将系统划分为子系统并使用从头算波函数方法来理解复杂环境中分子的激发态性质。在使用从头算量子化学研究非平凡环境中的分子复合物时，同时面临着不同的挑战。一个明显的问题是现有的（波函数）方法的急剧缩放，使得在实践中只能处理非常有限数量的原子。随着系统规模的增加，一个更微妙的问题是由于所涉及的分子数量而产生的状态和自由度的数量，因此，与所使用的方法无关，在超分子计算中对所有分子的显式处理通常会使化学激发的亚基的分析变得过于困难。嵌入方法给出了一个有用的分析方法，该方法将超系统划分为更小的亚基，从而留下非常有限数量的状态，这些状态根据定义被分配给某个分子，并且缩放问题被显著地减少。冷冻密度包埋（FDE）已被证明是一种有效的方法来划分由几个分子组成的复合物，所有子系统使用从头计算方法处理。这种方法的主要特点之一是允许一个系统的，一致的和严格的推导最常见的分子性质的波函数方法，避免特殊情况下处理某些属性，或需要重新参数化的半经验parameters.In这个项目中，我们将开发分析核梯度近似耦合集团单和双（RI-CC 2）FDE的基态和激发态。新方法可用于研究激发的起源及其对溶剂化壳复合物（激发态）几何结构的影响，同时可以区分显着移位的局部激发和“真正”的超系统效应，如碎片间电荷转移激发。该项目的主要应用是在小分子复合物中被明确的溶剂化分子包围，其中RI-CC 2方法是适用的。这产生了各种各样的有趣的复合物，例如从脱氧核糖核酸（DNA）二聚体到苯二聚体，即从氢键到范德华相互作用。特别地，感兴趣的系统是溶液中的准分子，其中如果需要考虑多于一个自由度，则激发态几何优化比单点扫描显著更有效。