Theorectical Studies of van der Waals Molecules

该项目由美国国家科学基金会理论与计算化学计划资助，研究分子间相互作用的现象。特拉华大学的Krzysztof Szalewicz教授及其合作者将进一步改进他们为二聚体相互作用开发的对称适应摄动理论（SAPT），并将推导出一个适用于三聚体的新版本。这一理论允许从四种基本相互作用方面对分子间电位进行透明的物理解释：静电、交换、感应和分散。该理论不存在基集叠加问题，计算效率比超分子多体摄动理论方法高。高水平的计算，最先进的分子间势能表面的实验相关范德华二聚体和三聚体将进行。这些研究将有助于理解范德华键形成的真实物理机制，以及导致最小值、隧道势垒和势各向异性的物理相互作用。这项工作预计将有助于解释实验数据，特别是在三体不可加性的情况下。该项目的一个重要部分将涉及旨在解决当前领域中有关稀有气体原子与各种分子（如氮、二氧化碳、水或氨）以及这些分子的二聚体相互作用的问题的应用。三聚体将包括稀有气体原子，Ar2-HF和水三聚体。目前对三体相互作用的理论认识是非常不令人满意的，特别是考虑到最近在这一领域的实验活动。SAPT方法提供了对非可加性进行物理分析并获得其精确数值的可能性。这个项目研究分子间相互作用的现象。这些相互作用比分子中原子之间的化学力要弱得多，但却导致了范围广泛的物理、化学和生物现象：从水的沸腾到遗传密码。标准的计算化学方法在描述化学键方面非常成功，但在描述这些分子间作用力时却不够。Szalewicz和合作者将开发和使用基于这些系统的量子力学描述的严格方法，以便对这些分子相互作用提供更完整的理解。

This project, supported by the NSF Theoretical and Computational Chemistry Program, investigates the phenomenon of intermolecular interactions. Prof. Krzysztof Szalewicz of the University of Delaware and collaborators will further improve symmetry-adapted perturbation theory (SAPT) developed by them for dimer interactions, and a new version applicable to trimers will be derived. This theory allows transparent physical interpretation of intermolecular potentials in terms of four fundamental interactions: electrostatic, exchange, induction, and dispersion. The theory is free from basis set superposition problems and is computationally more efficient than the supermolecular many-body perturbation theory approach. High-level calculations of state-of-the-art intermolecular potential energy surfaces for experimentally relevant van der Waals dimers and trimers will be performed. These studies will help provide an understanding of the real physical mechanism for the formation of van der Waals bonds and the physical interactions that are responsible for minima, tunneling barriers, and anisotropies of the potentials. This work is expected to assist interpretation of experimental data, particularly in the case of three-body nonadditivities. An important part of the project will involve applications aimed at resolving current problems in the field concerning interactions of rare gas atoms with various molecules such as nitrogen, carbon dioxide, water, or ammonia, as well as dimers of those molecules. The trimers will include rare gas atoms, Ar2-HF, and the water trimer. The current theoretical understanding of three-body interactions is very unsatisfactory, in particular in view of recent experimental activity in this field. The SAPT method offers the possibility of physical analysis of nonadditivities and of obtaining accurate numerical values for them. This project investigates the phenomenon of interactions between molecules. These interactions, much weaker than the chemical forces binding atoms in molecules, are responsible for an extensive range of physical, chemical, and biological phenomena: from the boiling of water to the genetic code. Standard computational chemistry methods, which are very successful in describing chemical bonds, are inadequate in describing these intermolecular forces. Szalewicz and collaborators will develop and use rigorous methods based on a quantum mechanical description of these systems in order to provide a more complete understanding of these molecular interactions.