Exploring Spectral Signatures of Molecular Vibrations

华盛顿大学的Anne B.McCoy教授得到了化学系化学理论、模型和计算方法(CTMC)项目的支持，以开发新的理论和计算工具，用于探索氢键系统中核量子效应的表现。氢键是无处不在的，常水(H2O)和重水(D2O)的性质往往有惊人的巨大差异。这些差异中的许多都归因于分子振动的量子力学性质。虽然知道这些影响的存在很容易，但量化它们要困难得多。安妮·麦考伊和她的研究小组开发了探索分子振动中的量子力学效应的工具，并通过与实验小组的合作，努力增强我们对这些效应的理解。她和她的研究小组正在开发的方法可以应用于最多20个原子的系统，这些系统足够小，可以进行详细计算，并与光谱实验进行比较，但也足够大，可以展示影响液态水或冰性质的核量子效应的类型。在这项工作的同时，Anne McCoy和她的团队正在开发可供社区使用的工具，以实现她所拥有的方法。她正在从事各种活动，致力于培养下一代物理化学家，包括通过担任国际分子光谱学研讨会国际咨询委员会主席和美国物理学会化学物理分会官员的角色，指导学生和促进早期职业科学家的工作。支持的工作重点是发展振动微扰理论和扩散蒙特卡罗方法，并使用这些方法来探索氢键系统中核量子效应的表现。振动微扰理论的工作重点是发展识别共振的方法，并探索三阶和更高阶修正对二阶(VPT2)结果的作用。这项工作的一个主要特点是探索哈密顿量在其中展开的坐标对从振动微扰理论获得的见解的影响。扩散蒙特卡罗(DMC)的工作集中于开发有效的程序，利用神经网络势来评估扩散蒙特卡罗中使用的势能，这些势能是基于从小的扩散蒙特卡罗模拟得到的几何形状来评估的。然后在更大的DMC研究中对这些潜在表面进行研究。这些研究的一个中心应用是探索核量子效应是如何通过对水团簇的研究在水中表现出来的。这项工作的重点是探索光谱、大振幅运动之间的关系，以及水和质子水系统的结构如何以及为什么随着氢气的变化而变化。这些研究的一个基本主题是开发可用于探索广泛系统的通用方法，并发展一般理解，以提供对氢键中的量子效应的更广泛的见解，这些效应超出了正在研究的特定系统。在这项工作中开发的代码是Anne McCoy和她的研究小组一直在开发的PyVibDMC和PyVibPTn代码的一部分。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Professor Anne B. McCoy of the University of Washington is supported by an award from the Chemical Theory, Models and Computational Methods (CTMC) program in the Division of Chemistry to develop new theoretical and computational tools that will be used to explore the manifestations of nuclear quantum effects in hydrogen-bonded systems. Hydrogen-bonding is ubiquitous, and there are often surprisingly large differences between properties of normal water (H2O) and heavy water (D2O). Many of these differences are attributed to the quantum mechanical nature of molecular vibrations. While knowing that these effects exist is easy to articulate, quantifying them is much more difficult. Anne McCoy and her research group develop tools for exploring quantum mechanical effects in molecular vibrations, and through collaborations with experimental groups has worked to enhance our understanding of these effects. The methods that she and her research group are developing can be applied to systems of up to 20 atoms that are small enough for detailed calculations and comparisons to spectroscopic experiments, but large enough to exhibit the types of nuclear quantum effects that affect properties of liquid water or ice. In parallel with this work, Anne McCoy and her group are developing tools that can be used by the community to implement the approaches she has. She is pursuing a variety of activities that focus on development of the next generation of physical chemists including mentoring students and promoting early career scientists through her roles as chair of the International Advisory Committee for the International Symposium on Molecular Spectroscopy and an officer of the American Physical Society’s Division of Chemical Physics.The supported work focuses on the development of vibrational perturbation theory and diffusion Monte Carlo approaches and using these approaches to explore the manifestations of nuclear quantum effects in hydrogen-bonded systems. The work on vibrational perturbation theory focuses on the development of approaches for identifying resonances and exploring the role of third and higher order corrections to the results obtained at second order (VPT2). A key feature of this work is the exploration of the impact of coordinates in which the Hamiltonian is expanded on the insights obtained from vibrational perturbation theory. The work on Diffusion Monte Carlo (DMC) focuses on the development of efficient procedures for evaluating the potential energies used in DMC using neural-network potentials, which are based on the geometries evaluated from small DMC simulations. These potential surfaces are then in larger DMC studies. A central application of these studies is an exploration of how nuclear quantum effects are manifested in water through studies of water clusters. This work focuses on probing relationships between spectra, large amplitude motions and how and why the structure of water and protonated water systems change with deuteration. A theme that underlies these studies is the development of versatile approaches that can be used to explore a broad range of systems, and to develop general understandings that provide broader insights in quantum effects in hydrogen bonding that extend beyond the specific systems that are being studied. The codes developed in this work are part of the PyVibDMC and PyVibPTn codes that Anne McCoy and her research group have been developing.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.