Direct Calculation of Activation Energies and Entropies for Chemical Dynamics

堪萨斯大学的Ward Thompson获得了化学系化学理论、模型和计算方法项目的奖励，以开发和应用确定化学动态过程的速率如何随温度变化的方法。 温度的影响使我们了解决定化学转化速率的因素。新开发的方法将提供一种在分子基础上分解这些物质的方法。 化学成分和熵对化学时标的影响也将被检查。 所提出的方法将在与材料和生物学相关的三个化学系统的动力学研究中进行测试：限制在纳米级无定形二氧化硅孔中的水，蛋白质水化壳中的水，以及参与氢键超分子组装并与之关联的水分子。 在拟议的工作中开发的方法将提供新的见解，这些问题，解决重要的开放问题的活力和熵的动力驱动力。 汤普森小组还将创建新的课程材料，以提高学生对化学动力学的理解和欣赏。汤普森小组将开发和应用直接计算化学中重要动力学过程的活化能和熵的理论方法。 方法将被调查1）确定分子的活化能的贡献，以产生详细的机制洞察到潜在的动力学; 2）直接确定的组成依赖的动态时间尺度; 3）严格的，直接计算的活化熵沿着与新的分子水平的见解。 这些方法是基于评估衍生物相对于温度（和其他热力学变量）的时间相关函数，从动态时间尺度，如速率常数或扩散系数，可以得到。 这些导数本身就是时间相关函数，可以直接从相同的分子动力学模拟中进行评估。 以这种方式，通常通过阿耳忒弥斯分析从多个温度下的计算获得的活化能或熵可以从单个温度下的模拟确定。 这种方法的一个关键优势是，它能够将活化能或熵严格分解为系统中存在的相互作用和运动的贡献，提供了否则无法获得的物理洞察力。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Ward Thompson of the University of Kansas is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to develop and apply methods for determining how the rates of dynamical processes in chemistry change with temperature. The effect of temperature gives insight into the factors that determine the rate of a chemical transformation. The newly developed methods will provide a way to decompose these on a molecule-by-molecule basis. The influences of the chemical composition and entropy on chemical timescales will also be examined. The proposed methods will be tested in investigations of dynamics in three chemical systems relevant to materials and biology: Water confined in nanoscale amorphous silica pores, water in the hydration shell of proteins, and water molecules participating in and associating with hydrogen-bonded supramolecular assemblies. The approaches developed in the proposed work will provide new insight into these problems by addressing important open questions about the energetic and entropic driving forces for the dynamics. The Thompson group will also create new course materials that improve student understanding of, and appreciation for, dynamics in chemistry.The Thompson group will develop and apply theoretical methods for directly calculating activation energies and entropies for dynamical processes important in chemistry. Methods will be investigated for 1) determining the molecule-by-molecule contributions to the activation energy to yield detailed mechanistic insight into the underlying dynamics; 2) directly determining the composition dependence of dynamical timescales; 3) the rigorous, direct calculation of the activation entropy along with new molecular-level insight. These approaches are based on evaluating derivatives with respect to temperature (and other thermodynamic variables) of the time correlation functions from which dynamical timescales, such as rate constants or diffusion coefficients, can be obtained. These derivatives are themselves time correlation functions and can be evaluated straightforwardly from the same molecular dynamics simulations. In this way, an activation energy or entropy that is normally obtained from calculations at multiple temperatures through an Arrhenius analysis can be determined from simulations at a single temperature. A key advantage is that this approach enables a rigorous decomposition of the activation energy or entropy into contributions from the interactions and motions present in the system, providing otherwise unavailable physical insight.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.