Collaborative Research: Noncovalently Bound Molecular Trimers: High-dimensional and Fully Coupled Quantum Calculations of their Vibrational Levels

Bacic（纽约大学）和Felker（加州大学洛杉矶分校）获得了化学学部化学理论、模型和计算方法项目的奖励，他们开发并实现了一种新颖而强大的方法，用于对氢键和范德华分子三聚体的振动特征态进行精确的高维和完全耦合量子计算。他们将专注于具有相当实际和基本重要性的现实分子复合体，并适合光谱研究，允许理论和实验之间的直接比较。他们的研究将导致更准确地描述在散装液体、分子固体和大气化学中起主要作用的非共价分子间相互作用，以及在这些环境中发生的过程。Bacic和Felker将继续通过指导研究生和本科生以及博士后研究人员组成的多样化和性别平衡的群体来促进包容性。他们将参与各种拓展活动，包括向未被充分代表的高中少数族裔学生进行科普演讲。Bacic和Felker将引入一种通用方法，该方法将首次实现对柔性或刚性单体的非共价结合分子三聚体的振动水平进行高维全耦合量子计算。他们将针对以下三类典型的氢键分子三聚体开发严格的量子束缚态方法。(1) 12D中柔性双原子分子的三聚体，如（HF）3和（HCl）3。(2)刚性小多原子分子（如（H2O）3）在12D中的三聚体。(3)刚性分子的两种混合三聚体，例如（HCl）（H2O）2和卤化物二水配合物X-(H2O)2 (X = Cl, Br， I)，分别在11D和9D。通过比较计算得到的振动能级和三聚体红外光谱中观察到的跃迁，他们将评估从头计算得到的三聚体势能面（PESs）中包含的非加性三体相互作用的准确性。此外，这样的比较将极大地帮助他们分配测量的红外光谱，这对于流态配合物是严重依赖于理论的。许多分子三聚体的分子间PESs，例如（H2O）3和X-(H2O)2 (X = Cl, Br， I)，表现出连接简并极小值的多个低势垒隧穿路径，从而产生复杂的隧穿分裂模式，在测量光谱中可以观察到。Bacic和Felker对三聚体分子间振动态的完全耦合量子计算将首次产生激发态的隧穿分裂。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Bacic (NYU) and Felker (UCLA) are supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop and implement a novel and powerful methodology for accurate high-dimensional and fully coupled quantum calculations of the vibrational eigenstates of hydrogen-bonded and van der Waals molecular trimers. They will focus on realistic molecular complexes of considerable practical and fundamental importance and amenable to spectroscopic investigations, allowing for direct comparison between theory and experiment. Their studies will lead to more accurate description of the noncovalent intermolecular interactions, which play a major role in bulk liquids, molecular solids, and atmospheric chemistry, and the processes that occur in these environments. Bacic and Felker will continue to foster inclusivity by mentoring diverse and gender-balanced groups of graduate and undergraduate students, as well as postdoctoral researchers. They will engage in a variety of outreach activities, including popular science presentations, to underrepresented high-school minority students. Bacic and Felker will introduce a general approach that will enable, for the first time, high-dimensional fully coupled quantum calculations of the vibrational levels of noncovalently bound molecular trimers, for either flexible or rigid monomers. They will develop rigorous quantum bound-state methodologies aimed at the following three classes of paradigmatic hydrogen-bonded molecular trimers. (1) Trimers of flexible diatomic molecules, e.g., (HF)3 and (HCl)3, in 12D. (2) Trimers of rigid small polyatomic molecules, e.g., (H2O)3, in 12D. (3) Two types of mixed trimers of rigid molecules, exemplified by (HCl)(H2O)2 and the halide dihydrate complexes X-(H2O)2 (X = Cl, Br, I), in 11D and 9D, respectively. Through comparison between the computed vibrational levels and the transitions observed in the infrared (IR) spectra of the trimers, they will assess the accuracy of the ab initio calculated nonadditive three-body interactions incorporated in the trimer potential energy surfaces (PESs). Moreover, such a comparison will help them greatly with the assignment of the measured IR spectra, which for fluxional complexes is heavily reliant on theory. The intermolecular PESs of many molecular trimers, e.g., (H2O)3 and X-(H2O)2 (X = Cl, Br, I), exhibit multiple low-barrier tunneling pathways connecting the degenerate minima, which give rise to intricate patterns of tunneling splittings, observable in the measured spectra. The fully coupled quantum calculations by Bacic and Felker of the intermolecular vibrational states of the trimers will for the first time yield the tunneling splittings in the excited vibrational states.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.