Chemical Bonding and Reactivity in Extended Systems and Molecules

康奈尔大学的罗尔德·霍夫曼在理论和计算化学计划的支持下开展研究，目的是(1)解释分子的电子结构，无论是离散的还是扩展的，这是成键中的难题，(2)对重要分子类中的化学键有一个定性的理解，重点是分子和扩展系统之间的关系，强调在有机和无机结构之间建立概念桥梁，(3)广泛和定性地研究表面和界面上的反应性问题，(4)预测具有不寻常性质的尚未合成的系统，以及(5)为应用量子化学设计更多的分析工具。所采用的方法将是定性(扩展休克尔法)和定量(密度泛函理论)可靠性的量子力学计算，以及构建解释的微扰理论装置。预计结果将为范围广泛的化学家、物理学家和材料科学家提供工具，以定性地分析和了解广泛的离散分子和扩展结构上的成键、结构和反应性。尽管量子化学的计算设备处于有可能实现对中等分子的预测化学精度的阶段，但化学界仍然强烈需要解释和增加理解。这些解释代表了对导致分子的结构、能量学和反应性的因素的一种便携的、定性的解释，也是本研究的目标。这样的计算可以用对广泛的科学界有用的化学概念来表述，例如电负性、轨道、静电学和空间效应。

Roald Hoffmann of Cornell University is supported by the Theoretical and Computational Chemistry Program to carry out research that aims to (1) explain the electronic structure of molecules, discrete or extended, that present puzzles in bonding, (2) develop a qualitative understanding of the chemical bonding in important classes of molecules, with a focus on relationships between molecular and extended systems, stressing the construction of conceptual bridges between organic and inorganic structures, (3) look broadly and qualitatively at problems of reactivity on surfaces and at interfaces, (4) predict as yet unsynthesized systems with unusual properties, and (5) devise further analytical tools for applied quantum chemistry. The methodology to be employed will be quantum mechanical calculations of both qualitative (extended Huckel method) and quantitative (density functional theory) reliability, as well as the apparatus of perturbation theory for constructing interpretations. Outcomes are expected to provide a wide range of chemists, physicists, and materials scientists with the tools to analyze and understand qualitatively bonding, structure, and reactivity over a wide range of discrete molecules and extended structures. Although the computational apparatus of quantum chemistry is at a stage where it is possible to attain predictive chemical accuracy for medium-sized molecules, there remains a strong need in the chemical community for explanations and increased understanding. These explanations represent a portable, qualitative accounting of the factors responsible for the structure, energetics, and reactivity of molecules, and are the goals of this research. Such accounting can be couched using chemical ideas that are qualitatively useful to the broad scientific community, such as electronegativity, orbitals, electrostatics, and steric effects.