Department of Chemistry and Henry Eyring Center for Theoretical Chemistry, University of Utah , Salt Lake City, Utah 84112, United States.
Department of Chemistry, University of California , Irvine, California 92697, United States.
J Am Chem Soc. 2017 May 24;139(20):7082-7088. doi: 10.1021/jacs.7b03143. Epub 2017 May 12.
Characterizing structural and phase transformations of water at the molecular level is key to understanding a variety of multiphase processes ranging from ice nucleation in the atmosphere to hydration of biomolecules and wetting of solid surfaces. In this study, state-of-the-art quantum simulations with a many-body water potential energy surface, which exhibits chemical and spectroscopic accuracy, are carried out to monitor the microscopic melting of the water hexamer through the analysis of vibrational spectra and appropriate structural order parameters as a function of temperature. The water hexamer is specifically chosen as a case study due to the central role of this cluster in the molecular-level understanding of hydrogen bonding in water. Besides being in agreement with the experimental data available for selected isomers at very low temperature, the present results provide quantitative insights into the interplay between energetic, entropic, and nuclear quantum effects on the evolution of water clusters from "solid-like" to "liquid-like" structures. This study thus demonstrates that computer simulations can now bridge the gap between measurements currently possible for individual isomers at very low temperature and observations of isomer mixtures at ambient conditions.
表征水在分子水平上的结构和相转变对于理解从大气中的冰核形成到生物分子的水合作用和固体表面的润湿等多种多相过程至关重要。在这项研究中，通过分析振动光谱和适当的结构有序参数作为温度的函数，使用展现化学和光谱准确性的多体水分子势能表面的最先进量子模拟，来监测水分子六聚体的微观熔化。水分子六聚体被特别选为案例研究，因为该簇在理解水中氢键的分子水平中起着核心作用。除了与非常低温下特定异构体的实验数据一致外，这些结果还提供了定量的见解，说明了在水团簇从“固态”到“液态”结构的演变过程中，能量、熵和核量子效应之间的相互作用。因此，该研究表明，计算机模拟现在可以弥合当前对于非常低温下单个异构体的测量和环境条件下异构体混合物的观察之间的差距。
