Accurate charge density determination in Zintl phases

Zintl-Klemm-Busmann概念是理解(极性)金属间化合物的结构和化学键的最有力的工具之一。所谓的锌相由正电性金属(碱、碱土或稀土)和电负性较强的p-块金属或半金属元素组成，例如三重金属、四重金属或五重金属。锌相中的化学键是通过正电性金属的价电子向电负性元素的正式、完整的电荷转移而合理化的。如果给出的电子数不足以满足八重态规则，则形成共价的、定域的、定向的2c2e键和多阴离子亚结构。这个项目的主要目的是通过实验测定Zintl相的电荷密度来评估这一概念。为了获得具有可比性的结果，研究将主要限于Ca-Si系统。通过电弧熔炼和高温技术可以合成足够质量的晶体。将研究使用化学传输反应的可能性。电荷密度将通过对低温、高分辨率X射线和中子衍射数据的精确处理而得到。除了用原子在分子中(AIM)形式分析形变密度和电子密度外，电子局域化函数(ELF)将由实验数据近似得到。这些研究将得到电子结构计算的补充，以便对化学键进行量子化学评估。锌相实验电荷密度的测定具有特别重要的意义，因为自从第一次征文以来就宣布了这一点。

One of the most powerful tools for the understanding of structures and chemical bonding in (polar) intermetallic compounds is the Zintl-Klemm-Busmann concept. So-called Zintl phases consist of an electropositive metal (alkali, alkaline earth, or rare earth) and a more electronegative p-block metallic or semimetallic element e. g. of the group of the triels, tetrels or pentels. The chemical bonding in Zintl phases is rationalized by a formal, complete charge transfer of the valence electrons of the electropositive metal to the electronegative element. If the number of donated electrons is not sufficient to fulfil the octet rule, covalent, localized, directional 2c2e-bonds and polyanionic substructures are formed. The main purpose of this project is the evaluation of this concept by experimental charge density determinations in Zintl phases. In order to obtain comparable results, the investigations will mainly be restricted to the system Ca-Si. Crystals of sufficient quality will be synthesized by arc melting and high-temperature techniques. The possibility of using chemical transport reactions will be investigated. The charge densities will be derived from an accurate treatment of low temperature, high- resolution X-ray and neutron diffraction data. Apart from the analysis of the deformation density and of the electron density with the Atoms-In-Molecules (AIM) formalism, the Electron Localization Function (ELF) will be approximated from the experimental data. These investigations will be supplemented by electronic structure calculations for a quantum chemical evaluation of the chemical bonding. The determination of the experimental charge density in Zintl phases is of particular importance, as it has been announced since the first call for papers.