Development and Applications of Electronic Structure Methods for Open-shell and Electronically Excited Species with Strongly Interacting States of Different Character

南加州大学的安娜·克雷洛夫在理论和计算化学计划的支持下，开发了开壳层和电子激发物种的电子结构方法，特别是那些具有不同性质的强相互作用电子态的物种。该计划充分利用了PI在开发新的运动方程(EOM)耦合簇(CC)方法方面的最新进展，这些方法将这一稳健而有效的技术扩展到处理自由基、三自由基和键断裂。计划进行以下方法学发展：(I)探索Fock空间的更高部分(例如，双自旋翻转、自旋翻转-(双)电离等)。将EOM扩展到在多个键断裂时遇到更广泛简并的情况；(Ii)包括更高的激发以实现化学精度；(Iii)开壳CC和EOM波函数的自旋自适应，以提高在有问题的情况下的精度，例如自旋污染或不稳定的参考。新的方法将用于研究燃烧和大气化学中涉及的开壳物种的电子结构，以及实际相关的自由基阴离子反应(即，苯并和富烯阴离子)，继续与实验小组合作。这项研究有望带来对环境和技术重要性问题的新见解，例如与大气和合成化学有关的化学反应系统。这项研究还包括计算机代码设计和实现的强大组成部分，并将帮助学生为高科技行业的职业生涯做好准备，在高科技行业，使用复杂计算工具解决复杂问题的能力受到高度重视。新的计算机软件将被集成到广泛可用的电子结构程序中，使这些结果可供广大化学界使用。

Anna Krylov of the University of Southern California is supported by the Theoretical and Computational Chemistry Program to develop electronic structure methodology for open-shell and electronically excited species, in particular for those with strongly interacting electronic states of different nature. The proposed program capitalizes on the PI's recent advances in developing new equation-of-motion (EOM) coupled-cluster (CC) methods, which extend this robust and efficient technique to treat diradicals, triradicals, and bond-breaking. The following methodological developments are planned: (i) exploring higher sectors of the Fock space (e.g., double spin-flip, spin-flip - (double) ionization, etc.) to extend EOM to situations with more extensive degeneracies encountered upon multiple bond-breaking, in transition metals and polyradicals; (ii) including higher excitations to achieve chemical accuracy; (iii) spin-adaptation of open-shell CC and EOM wave functions to improve accuracy in problematic cases such as spin-contaminated or unstable references. The new methodology will be applied to study electronic structure of open-shell species involved in combustion and atmospheric chemistry as well as practically relevant radical anionic reactions (i.e., benzyne and fulvene anions), in continuing collaborations with experimental groups. This research is expected to lead to new insights into problems of environmental and technological importance, for example chemical reaction systems that are relevant to atmospheric and synthetic chemistry. This research also includes a strong component of computer code design and implementation, and will help prepare students for careers in high-tech industries where the ability to solve complex problems using sophisticated computational tools is highly valued. New computer software will be integrated into widely available electronic structure programs, making these results available to the broad chemistry community.