Accurate charge density determination in Zintl phases

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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.