Exploring the Connections between the Nonlinear Spectroscopy and the Potential Energy Landscapes of Liquids

Richard M.布朗大学的斯特拉特得到了化学系化学理论，模型和计算方法项目的支持，因为他研究了液体混合物，液晶和过冷液体中异常缓慢的分子动力学之间的关系，以及这些系统的势能景观的全球特征。虽然缓慢的动力学通常是可以理解的，因为需要重新排列单个化学键或克服势能面上的其他局部瓶颈，但在许多最有趣的情况下，问题更多的是难以定位和穿越即使是最有效的全球路径。这项工作研究了如何利用计算机模拟来表征这些最有效的（“测地线”）途径，并试图建立从这些途径获得的信息之间的定量联系，并从新的非线性光谱。光谱研究的一半集中在溶质泵/溶剂探针光谱，特别是，因为这些光谱有可能揭示如何广泛的溶剂结构可以重新排列在一个新的电子激发溶质的存在。通过计算优先溶剂化混合物，染料掺杂液晶和易碎玻璃形成液体的预期光谱，并将结果与测地线景观分析的结果进行比较，研究人员希望了解光谱学如何用于发现这些特别缓慢的系统的势能景观的独特之处。斯特拉特教授和他的研究小组正在开发计算方法，以探索在液体混合物，液晶和过冷液体中看到的缓慢分子动力学与这些系统的势能景观的某些特征之间的关系。 势能景观是系统中原子的相互作用能，作为原子之间距离的函数。 斯特拉特的研究重点是如何找到通过这些景观的最有效的途径;这些途径决定了原子的实际运动。 斯特拉特还开发了理论方法来预测和分析光谱，帮助我们了解溶剂如何与处于激发电子状态的分子反应。这项研究的最终回报可能是对涉及缓慢分子重排的两个非常重要的实际问题的有用见解：确定玻璃状和无定形材料的性质，以及了解蛋白质如何以及何时错误折叠。无定形物质的韧性和易加工性通常使它们成为理想的商业材料，但令人惊讶的是，关于玻璃化的许多科学基础几乎没有共识。同样，抵抗折叠成有序结构的蛋白质对生物体至关重要，但其中一些以无定形方式折叠的蛋白质是关键人类健康问题的标志，包括阿尔茨海默病。这项研究涉及大学生作为研究合作者，从而丰富了他们的科学教育。

Richard M. Stratt of Brown University is supported by the Chemical Theory, Models, and Computational Methods program in the Chemistry division for his research on the relationships between the unusually slow molecular dynamicsseen in liquid mixtures, liquid crystals, and supercooled liquids, and the global features of the potential-energy landscapes of these systems. While slow dynamics is often understandable as a consequence of the need to rearrange individual chemical bonds or surmount other local bottlenecks on the potential energy surface, in many of the most interesting cases, the issue is more the difficulty in locating and traversing even the most efficient global pathways through the landscape. This work investigates how computer simulations can be used to characterize these most efficient ("geodesic") pathways and attempts to forge quantitative connections between the information garnered from these pathways and that available from novel nonlinear spectroscopies. The spectroscopic half of the research is focused on solute pump/solvent-probe spectra, in particular, because those spectra have the potential to reveal how broad swaths of solvent structure can rearrange in the presence of a newly electronically excited solute. By computing the spectra expected from preferentially solvating mixtures, dye-doped liquid crystals, and fragile-glass-forming liquids, and comparing the outcomes with the results of a geodesic landscape analysis, the researchers hope to learn how spectroscopy can be used to discover what is so unique about the potential energy landscapes of these especially slow systems. Professor Stratt and his research group are developing computational methods to explore the relationship between the slow molecular dynamics seen in liquids mixtures, liquid crystals and supercooled liquids and certain features of the potential energy landscapes of these systems. A potential energy landscape is the interaction energy of the atoms in the system as a function of the distances between the atoms. Stratt's research focuses on how to find the most efficient pathways through these landscapes; such pathways determine the actual motions of the atoms. Stratt also develops theoretical methods to predict and analyze spectra that help us to understand how solvents react to molecules that are in an excited electronic state. The eventual payoff for this research may be useful insight into two enormously important practical problems involving slow molecular rearrangements: determining the properties of glassy and amorphous materials, and understanding how and when proteins fold incorrectly. The toughness and ease of processing of amorphous substances often makes them ideal commercial materials, but there is surprisingly little consensus about many of the scientific fundamentals of glassiness. Similarly, proteins that resist folding into well-ordered structures are essential to living organisms, but some of those that fold in an amorphous fashion are markers of critical human health problems, including Alzheimer's disease. The research involves undergraduates as research coworkers, thereby enriching their scientific education.