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

东南路易斯安那大学的托马斯·索默菲尔德（Thomas Sommerfeld）获得了化学学部化学理论、模型和计算方法项目以及美国国家科学基金会EPSCoR办公室的奖励，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粘合在一起的粘合剂。然而，电子胶的类比只能到此为止，因为太少或太多的胶都会削弱一个键，而在原子的永久运动中，弱键可能会断裂。换句话说，向分子中加入一个电子通常会削弱它的化学键，由此产生的所谓临时阴离子可能会发生化学键断裂，或者重新释放多余的电子。这种反应被应用或自然发生的具体例子有：等离子化学和等离子蚀刻，电离层中的化学，电离辐射对活组织的损害，电子束的癌症治疗，以及溶剂化电子的还原反应，即所谓的桦树还原。这个研究项目支持临时阴离子的计算机模型的发展，临时阴离子是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。为了让本科生了解这项研究，Sommerfeld博士还设计了一些教育性的小项目，这些小项目与当前的主要项目只是间接相关，但可以用标准的量子化学方法来解决，这样他的学生就可以一步一步地进入研究领域。在这个项目中，索默菲尔德博士研究电子亚稳态，即所谓的共振态，或者简单地说，共振。一方面，他开发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。计算共振的能量和有限寿命对于量子化学来说仍然是一个非常具有挑战性的任务，因为它结合了电子散射和电子相关问题。为了解决连续体方面的问题，Sommerfeld博士要么使用络合吸收电位，要么使用耦合常数的解析连续方法。为了解决相关方面的问题，他使用了一种与运动方程耦合簇方法密切相关的电子结构方法——对称适应簇构型相互作用方法。特别强调的一点是，在耦合常数解析连续法中，在哈密顿量中加入了人工稳定势。Sommerfeld博士的目标是确定短期稳定潜力，以改善随后的分析-延续步骤。在应用方面，Sommerfeld博士的目标是检查共振态，其电子结构与封闭壳中性的不同，要么是单孔（类俄格共振），要么是单激发（如Penning电离或共振光剥离）。对于这些共振，以平衡的方式处理电子相关是特别具有挑战性的。Sommerfeld博士研究嵌入在小分子簇中的临时阴离子共振，目的是确定与嵌入分子的相互作用强度（永久偶极子、高阶多极子、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.