The quantum mechanics of small molecules nanoconfined in complex chemical environments

在这个由化学系化学结构、动力学和机制A项目资助的项目中，纽约大学的Zlatko Bacic教授和Mark Tuckerman教授正在进行理论计算，这些分子被限制在由其他分子形成的笼中，或者被限制在单个C60“Buckyball”分子中。他们感兴趣的是了解水（H2O）、氢（H2）和其他小分子在有限空间内是如何运动的。这一理论研究将改进对实验测量结果的解释，例如一种称为非弹性中子散射（INS）的技术的结果。它还将在分子水平上对材料特性的控制（用于先进的“纳米电子学”应用）产生影响，并可能为能源技术设计高效经济的储氢介质。两名研究生作为研究人员直接参与了这个项目。本研究的概念进展和新成果将被整合到本科教材中。最后，在这个项目中取得的方法发展将被纳入主要研究人员的用户友好软件工具中，这些工具将免费提供给一般社区。在这些研究中实施了一系列复杂的理论和计算方法，其中一些是在实现该项目中开发的，从多维束缚态和散射方法到路径积分分子动力学（PIMD）模拟。利用新开发的纳米约束多原子分子INS光谱量子模拟方法，高精度地计算了C60约束中H2O的INS光谱。C60是一个由高量子水偶极子组成的非凡的三维立方晶格，每一个都被限制在C60内部，对C60晶体中的水进行了PIMD模拟，揭示了它的介电特性和自由能量学，包括由多体偶极相关引起的铁电相变。路径积分模拟还探讨了H2和D2分子在sII包合物水合物（简单和二元）中自由能量和近似扩散速率的温度和压力依赖性，考虑了量子效应和框架灵活性。这些研究解决了分子氢在量子体系中扩散的基本问题，在化学和结构复杂的环境中。凝聚相效应的量子处理，包括框架水分子的质子无序，对sII笼形水合物中H2的“咔咔”动力学和INS光谱的影响，解决了宿主环境中客体分子的动力学和光谱特性如何演变并接近其体积极限的一般问题。

In this project funded by the Chemical Structure, Dynamics and Mechanisms A program in the Division of Chemistry, Professors Zlatko Bacic and Mark Tuckerman of New York University are performing theoretical calculations on molecules confined in cages formed by other molecules, or within a single C60 "Buckyball" molecule. They are interested in understanding how molecules such as water (H2O), hydrogen (H2) and other small molecules move when they are in restricted spaces. This theoretical study will improve the interpretation of experimental measurements, for example the results of a technique called inelastic neutron scattering (INS). It will also have implications for the control of material properties at the molecular level (for advanced "nanoelectronics" applications), and possibly for the design of efficient and economical hydrogen storage media for energy technologies. Two graduate students are directly involved as researchers in this project. The conceptual advances and new results from this research will be integrated into educational materials for undergraduates. Finally, methodology developments achieved in this project will be incorporated into the Principal Investigators' user-friendly software tools that will be made freely available to the general community.An array of sophisticated theoretical and computational approaches, some developed in the realization of this project, ranging from multidimensional bound-state and scattering methods to path-integral molecular dynamics (PIMD) simulations, is implemented in these investigations. The INS spectra of H2O confined in C60 are calculated with high accuracy utilizing the newly developed methodology for quantum simulation of the INS spectra of nanoconfined polyatomic molecules. The PIMD simulations of the crystalline H2O in C60, an extraordinary 3D cubic lattice of highly quantum H2O dipoles, each confined inside C60, shed light on its dielectric properties and free energetics, including the ferroelectric phase transition, arising from the many-body dipolar correlations. Path-integral simulations also probe the temperature and pressure dependence of the free energetics and approximate diffusion rates of H2 and D2 molecules in the sII clathrate hydrates, simple and binary, accounting for quantum effects and framework flexibility. These studies address the fundamental problem of the diffusion of molecular hydrogen in the quantum regime, inside a chemically and structurally complex environment. Quantum treatment of the condensed-phase effects, including the proton disorder of the framework water molecules, on the "rattling" dynamics and the INS spectra of H2 in the sII clathrate hydrate addresses the general question of how the dynamical and spectroscopic properties of guest molecules inside a host environment evolve and approach their bulk limits.