Environment-Dependent Energetics of Ionically Bonded Metals

9971476Carlsson这笔赠款支持对具有离子键的金属原子的电子结构的理论研究。具有离子键构型的金属原子存在于从陶瓷到生物分子材料等大量具有重要技术意义的材料中。电子效应在许多这类材料的结构和功能中都很重要，例如决定铜在铜氧化物材料中的正方配位。现有的基于经典力场的离子结合金属模拟以不确定精度的能量项来处理电子效应。这里的研究使用一种近似的量子力学分析来开发出可靠地处理电子效应的力场。对于过渡金属，基于d-络合物宽度的矩展开被用来发展类似于“改进的嵌入原子方法”的能量函数。能量的角度依赖关系可以用余弦角的四次多项式来表示，其中角是以过渡金属为中心的键角。对于非过渡金属，四阶微扰展开被用来产生角势，其函数形式将与晶体结构和小分子的精确密度泛函计算的结果相吻合。由此产生的能量函数将被合并到离子材料中的金属和附着在共价框架上的金属的现有力场中。改进后的力场将用于分析沸石结构中过渡金属周围的局域结构和自组装生物分子材料中金属离子的能量学。这项研究将与丹麦技术大学、国家标准与技术研究所和福特汽车公司合作进行。%这笔赠款支持对具有离子键的金属原子的电子结构的理论研究。乍一看，纯金属中的金属原子通过“金属键”结合在一起。然而，所有的金属键都有一定程度的电离性，即静电吸引。具有离子键构型的金属原子存在于从陶瓷到生物分子材料等大量具有重要技术意义的材料中。这项研究将开发准确的方法来确定金属键和离子键之间的相互作用。将考虑两个测试案例：本质离子环境中的金属原子(沸石)和共价环境中的金属原子(生物分子材料)。这项研究将与丹麦技术大学、国家标准与技术研究所和福特汽车公司合作进行。

9971476CarlssonThis grant supports theoretical research on the electronic structure of metal atoms with ionic bonding. Metal atoms in ionic bonding configurations occur in a large number of technologically important materials ranging from ceramics to biomolecular materials. Electronic effects are important in the structure and function of many of these materials, for example in determining the square coordination of copper in copper-oxide materials. Existing simulations for ionically bound metals based on classical force fields treat electronic effects with energy terms of uncertain accuracy. The research here uses an approximate quantum-mechanical analysis to develop force fields that treat electronic efects reliably. For transition metals, a moment expansion based on the width of the d-complex is used to develop an energy function similar to the "modified embedded-atom method." The angular dependence of the energy is obtained as a fourth-order polynomial in cosine theta, where theta is a bond angle centered on the transition metal. For non-transition metals, a fourth-order perturbation expansion is used to generate angular potentials whose functional forms will be fit to results from accurate density-functional calculations, for crystalline structures and small molecules. The resulting energy functions will be incorporated into existing force fields for metals in ionic materials and for metals attached to covalent frameworks. The improved force fields will be applied to the analysis of the local structure around transition metals in zeolite structures and to the energetics of metal ions in self-assembled biomolecular materials. The research will be done in cooperation with the Danish Technical University, the National Institute for Standards and Technology and the Ford Motor Company.%%%This grant supports theoretical research on the electronic structure of metal atoms with ionic bonding. At first glance, metal atoms in pure metals are bound together by the "metallic bond." However, all metallic bonds have some degree of ionicity, or electrostatic attraction. Metal atoms in ionic bonding configurations occur in a large number of technologically important materials ranging from ceramics to biomolecular materials. This research will develop accurate methods to determine the interplay between metallic and ionic bonding. Two test cases will be considered: metal atoms in an intrinsically ionic environment (zeolites) and metal atoms in a covalent environment (biomolecular materials). The research will be done in cooperation with the Danish Technical University, the National Institute for Standards and Technology and the Ford Motor Company.***