RUI: Development of Computational Methods and Applications to Molecules in Microsolvation Environments.

东南路易斯安那大学的Thomas Sommerfeld得到了化学部化学理论、模型和计算方法项目和NSF EPSCoR办公室的支持，该奖项旨在研究额外的电子如何帮助打破化学键。化学键本身是原子之间共享的电子，可以被认为是将分子中的原子连接在一起的胶水。然而，电子胶的类比仅限于此，因为太少和太多的胶水都会削弱键，而弱键可能会在原子的永久运动中断裂。换句话说，向分子中添加电子通常会削弱其键，由此产生的所谓临时阴离子可能会发生键断裂，或者重新释放额外的电子。应用或自然发生这种反应的具体例子有：等离子体化学和等离子体蚀刻、电离层中的化学、电离辐射对生物组织的损害、电子束治疗癌症以及与溶解电子的还原反应，即所谓的Birch还原。这项研究项目支持开发暂时性阴离子的计算机模型，临时性阴离子是在这些电子诱导反应中形成的第一个中间体。这项研究是与合作者和本科生研究人员一起进行的。为了向本科生介绍这项研究，Sommerfeld博士还设计了教育迷你项目，这些项目只与当前的主项目间接相关，但可以用标准的量子化学方法解决，这样他的学生就可以一步一步地被介绍到研究领域。在这个项目中，索默菲尔德博士研究了电子亚稳态--即所谓的共振态，或者简称为共振。一方面，他发展了从头算方法来表征共振，另一方面，他将新开发的方法应用于选定的应用中。对于量子化学来说，计算共振的能量和有限寿命仍然是一项众所周知的具有挑战性的任务，因为它将电子散射和电子关联问题结合在一起。为了解决连续体方面的问题，索默菲尔德博士要么使用复合吸收势，要么使用analytic-continuation-in-the-coupling-constant方法。为了解决关联方面，他使用了对称性适应的团簇组态相互作用方法，这是一种与运动方程耦合团簇方法密切相关的电子结构方法。特别要强调的一点是，在analytic-continuation-in-the-coupling-constant方法中给哈密顿量添加了人工稳定势。Sommerfeld博士的目标是确定一种短期稳定潜力，以改进后续的分析-继续步骤。在应用方面，Sommerfeld博士的目标是研究共振态，这些共振态的电子结构与闭壳中性的不同，要么是单空穴(俄歇类共振)，要么是一次激发(例如潘宁电离或共振光脱离)。对于这些共振，以平衡的方式处理电子关联特别具有挑战性。Sommerfeld博士研究嵌入在小分子簇中的暂时性阴离子共振，目的是确定与嵌入分子的相互作用强度(永久偶极、高阶多极、色散)相关的共振参数变化的趋势。

Thomas Sommerfeld of Southeastern Louisiana University is supported by an award from the Chemical Theory, Models and Computational Method program in the Chemistry Division and the NSF EPSCoR office to investigate how extra electrons aid in breaking chemical bonds. Chemical bonds themselves are electrons shared between atoms and can be thought of as a glue holding the atoms in a molecule together. The electron-glue analogy, however, only goes so far, because a bond can be weakened by both too little and too much glue, and weak bonds can be cleaved during the permanent motion of the atoms. In other words, adding an electron to a molecule generally weakens its bonds, and the resulting so-called temporary anion may undergo either bond cleavage or, alternatively, reemit the extra electron. Concrete examples where this reaction is applied or happens naturally are: plasma chemistry and plasma etching, chemistry in the ionosphere, damage to living tissue by ionizing radiation, cancer therapy with electron beams, and reduction reactions with solvated electrons, the so-called Birch reduction. This research project supports the development of computer models of the temporary anion, the first intermediate formed in these electron-induced reactions. This research is carried out with collaborators and with undergraduate researchers. In order to introduce undergraduates to this research, Dr. Sommerfeld also designs educational mini-projects, which are only indirectly related to the current main project, but can be addressed with standard quantum chemistry methods, so that his students can be introduced to the research area step-by-step. In this project Dr. Sommerfeld studies electronically metastable states - so called resonance states or, simply, resonances. On the one hand, he develops ab initio methods to characterize resonances, and on the other hand he applies the newly developed methods in selected applications. Computing both the energy and finite lifetime of a resonance is still a notoriously challenging task for quantum chemistry, because it combines an electron-scattering with an electron-correlation problem. To address the continuum aspect, Dr. Sommerfeld either uses complex-absorbing-potentials or the analytic-continuation-in-the-coupling-constant method. To address the correlation aspect, he uses the symmetry-adapted-cluster configuration-interaction method, an electronic structure method closely related to the equation-of-motion coupled-cluster method. One particular point of emphasis is the artificial stabilizing potential added to the Hamiltonian in the analytic-continuation-in-the-coupling-constant method. Dr. Sommerfeld aims to identify a short-range stabilizing potential that improves the subsequent analytic-continuation step. On the application side Dr. Sommerfeld's goals are to examine resonance states, which differ in electronic structure from a closed-shell neutral either by one-hole (Auger-like resonances) or by one excitation (e.g. Penning ionization or resonant photodetachment). For these resonances, treating electron correlation in a balanced way is particularly challenging. Dr. Sommerfeld studies temporary anion resonances embedded in small molecule clusters with the goal of identifying trends in the change of the resonance parameters associated with the interaction strength (permanent dipole, higher order multipoles, dispersion) of the embedding molecules.