Renewal of "Advancing Quantum Crystallography: Visualisation and Characterisation of Chemical Reactions via Diffraction Experiments": From Model Systems to Real Systems – from Molecules to Materials

量子晶体学是衍射实验和波函数到单一的研究工具的综合组合。近几年来，它已发展成为一个独立的新的研究领域。我们对该领域的贡献是X射线波函数精化（XWR）方法。在最初的Emmy Noether项目中，我们展示了XWR如何解决X射线结构测定和实验电子密度研究的长期问题，特别是关于氢原子和极性键的正确和准确描述。我们现在已经成功完成了XWR在分子化学中的方法和软件开发。因此，在更新项目的第一部分，我们专注于XWR在与氢原子相关的化学问题中的应用，这些问题无法用任何其他方法解决。我们将研究喹诺酮N-氧化物中的质子转移互变异构现象，这对它们的抗生素活性的作用模式是决定性的。我们也将研究C-H键的活化，通过agostic相互作用在钛酰胺。在这两类化合物中，氢原子的精确定位以及随后的能量和成键分析迄今为止还不可能，但XWR提供了理想的能力来做到这一点，从而回答了悬而未决的问题。在第二部分中，XWR将扩展到材料科学。许多技术上感兴趣的材料是扩展固体，即分子波函数不适合的周期性化合物。此外，它们不能形成足够大的单晶用于常规X射线结构测定，即只有粉末衍射是可行的。因此，我们将开发周期性XWR的技术，利用极端本地化的分子轨道和Wannier功能，导致极端本地化的Wannier功能，ELWF。此外，我们将开发一个迭代XWR Rietveld细化，可以执行一个改进的粉末样品的结构测定。通过结合这两种新开发的方法，XWR的应用扩展固体的粉末将是可能的。这将首次允许在亚原子水平上实验性地研究粉末的材料特性，重点是结合方面。我们将开始与方钴矿型材料的热电性能和莫来石型材料的热致变色性能的调查。

Quantum Crystallography is an integrative combination of diffraction experiments and wavefunctions into single research tools. It has developed into an independent new research field in the last few years. Our contribution to the field is the method X-ray Wavefunction Refinement (XWR). In the original Emmy Noether project, we have shown how XWR can solve long-standing problems of X-ray structure determination and experimental electron-density research, especially concerning the correct and accurate description of hydrogen atoms and polar bonds. We have now successfully finalised method and software development in XWR for molecular chemistry.In the first part of the renewal project, we thus focus on applications of XWR to chemical problems related to hydrogen atoms that cannot be solved with any other approach. We will investigate prototropic tautomerism in quinolone N-oxides, which is decisive for the mode of action of their antibiotic activity. We will also study C-H bond activation through agostic interactions in titanium amides. In both classes of compounds, the accurate localisation of hydrogen atoms and subsequent energetic and bonding analyses have not been possible so far, but XWR offers ideal capabilities to do so and hence to answer the open questions.In the second part, XWR will be extended to materials science. Many materials of technical interest are extended solids, i.e. periodic compounds for which molecular wavefunctions are not suitable. Moreover, they do not form single crystals large enough for routine X-ray structure determination, i.e. only powder diffraction is viable. Therefore, we will develop periodic XWR by utilising the techniques of extremely localised molecular orbitals and Wannier functions leading to extremely localised Wannier functions, ELWFs. In addition, we will develop an iterative XWR-Rietveld refinement which can perform an improved structure determination from powder samples. By the combination of both newly developed methods, application of XWR to powders of extended solids will be possible. This will for the first time allow the study of material properties from powders experimentally on the subatomic level focused on bonding aspects. We will begin with an investigation of thermoelectric properties of a skutterudite-type and thermochromic properties of a mullite-type material.