合金单晶材料的电子结构新理论：超原子晶体

Chemical bonding is the soul of chemistry, which gives "the sense of chemistry" to chemist, and so the structure and properties of complex molecules and solids can be understood. However, the geometric and electronic structures of metal can only be roughly described by metallic bond, that is, the free valence electrons are shared by metallic cations. The metal clusters with magic electronic numbers keep high stability. They are defined as superatoms due to their similar electronic structures and chemical reaction properties as simple atoms. Super valence bond (SVB) model further extend the superatom concept, which points out that two superatoms could compose a superatomic molecule by sharing electron pairs. In this project, we will extend SVB theory to the study of alloy crystal. We think that alloy crystal can be seen as superatomic crystal composed by superatom clusters via superatom-superatom bonding. Firstly, we will develop the method for the chemical bonding analysis of solid. Then, the idea of superatomic crystal will be verified by using Cu5Zn8 alloy crystal as test case. Finally, this method will be extended to general cases. The language of chemical bond is pulled in the area of alloy crystal by superatomic crystal model, and the geometry and properties of alloy can be understood by "the sense of chemistry", which can give scientific explanation to this engineering issue.

化学键是化学的灵魂，它给了化学家“化学感觉”，从而可以直观地理解各种复杂分子及原子晶体的结构及性质。而金属的几何及电子结构往往只能通过金属键进行泛泛地描述，即金属阳离子共享自由流动的价电子。具有幻数电子数的金属团簇表现出很高的稳定性，并具有与简单原子类似的电子结构及化学反应特性，可以看做一个超原子。超级共价键理论进一步拓展了超原子模型，认为超原子团簇可以通过共用电子对成键，构成超原子分子。本项目拟把超级共价键理论从金属团簇拓展到合金单晶材料中，认为合金单晶可以看做由超原子团簇通过超原子成键构成的超原子晶体。本项目首先搭建周期性体系成键分析平台，然后以Cu5Zn8单晶固体为突破口，验证超原子晶体理论，最后再拓展到一般合金单晶材料。超原子晶体模型把化学键的语言引入合金单晶研究领域，通过“化学感觉”理解其结构性质，从而为这一工程问题提供科学理论指导。

超原子这一概念吸引了物理化学家的广泛兴趣。基于超原子模型，金属团簇中的价电子可以自由地在整个团簇中离域，而团簇整体可以看作一个超级原子，其在电子结构及化学反应等方面都与对应的简单原子类似。超原子概念把元素周期表被从二维扩展到三维，从而大大丰富了化学的内涵。我们在前期工作中提出了超级共价键理论，认为电子并不会在整个团簇中离域，而是分属于多个超级原子，并且超级原子之间通过共享电子对形成超级共价键。本项目进一步发展、完善了超级共价键理论，提出了多超原子分子、超原子间的多中心键等模型。建立了超原子晶体模型，并且把该理论拓展到共轭大π体系中，建立了2D超原子分子模型。目前，超级共价键理论已为理论化学界所认可。在本项目的资助下，在NSR, JPCL, Nanoscale等国内外主流学术期刊发表SCI论文37篇，毕业博士2人、硕士11人。

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