Dynamics in Complex Systems: Computer Simulation of the Migration of Ions and Neutrals in Zeolites

加州大学圣巴巴拉分校的Horia Metiu在理论和计算化学项目的支持下，对沸石内部的离子和水分子进行了计算机模拟，并利用这些结果来探索物种是如何通过沸石运动的。同时，质子转移速率将被计算，完整的动力学描述和机制将被评估。严谨的方法将应用于小单元沸石，具体研究钠离子和水通过钠石的迁移以及氨与酸性钙辉石的反应。这些过程在工业应用中广泛使用，但在原子水平上对它们知之甚少。所有的能量计算都将用密度泛函理论进行，它考虑了固体的整个单位胞。用相关函数理论或过渡态理论计算重要过程的速率常数。结果将用于动力学蒙特卡罗程序来模拟迁移和动力学在很长的时间和空间尺度。预计计算沸石内部分子性质的能力将得到提高，这种方法将有助于工业过程的合理设计。沸石是结晶的多孔固体，能够吸收内部的各种分子。这种吸收是有选择性的（某些分子比其他分子更受欢迎），这种选择性可以用来分离各种气体，从气流中去除有害产物，或者用良性离子代替不需要的离子。沸石和它们吸收的客体分子相互作用强烈到足以在沸石框架内引起不寻常的化学反应。这种性质具有重要的实际意义，在石油工业中被用来改变各种产品的碳氢化合物含量。这个计算机模拟项目的结果将提高对沸石内部分子运动速度的理解，是什么决定了吸收选择性，是什么导致了被吸收物质的化学行为的变化。

Horia Metiu of UC Santa Barbara is supported by the Theoretical and Computational Chemistry Program to perform computer simulations of forces acting on ions and water molecules inside a zeolite, and to use these results to explore how the species move through the zeolite. Also, proton transfer rates will be calculated, and complete kinetic descriptions and mechanisms will be evaluated. Rigorous methodology will be applied to small unit cell zeolites, with specific studies of sodium ion and water migration through sodalite and the reaction of ammonia with acidic chabazite. These processes are widely used in industrial applications, yet very little is known about them at an atomic level. All energy calculations will be performed with density functional theory, which considers the full unit cell of the solid. Rate constants of the important processes will be calculated using correlation function theory or transition state theory. The results will be used in a kinetic Monte Carlo program to simulate migration and kinetics over very long time and space scales. It is anticipated that the ability to calculate the properties of molecules inside zeolites will be improved to the point that this methodology will assist in the rational design of industrial processes. Zeolites are crystalline, porous solids that have the ability to absorb inside them a variety of molecules. This absorption is selective (certain molecules are preferred to others) and the selectivity can be used to separate various gases, to remove noxious products from a gas stream, or to replace undesirable ions with benign ones. Zeolites and their absorbed guest molecules interact strongly enough to induce unusual chemical reactions within the zeolite frame. This property has practical importance and is exploited to modify the hydrocarbon content of various products in the oil industry. The outcomes from this computer simulation project will improve the understanding of how fast molecules move inside a zeolite, what determines absorption selectivity, and what causes changes in the chemical behavior of the absorbed species.