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

量子结晶学是将衍射实验和波函数综合成单一研究工具的一门学科。近几年来，它已经发展成为一个独立的新的研究领域。我们在这一领域的贡献是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如何解决长期存在的X射线结构确定和实验电子密度研究问题，特别是关于氢原子和极键的正确和准确描述。我们现在已经成功地完成了分子化学的XWR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在与氢原子有关的化学问题上的应用，这些问题是任何其他方法无法解决的。我们将研究喹诺酮类N-氧化物中的原性互变异构，这对它们的抗生素活性的作用方式是决定性的。我们还将研究钛酰胺中C-H键的活化。在这两类化合物中，到目前为止还不可能准确地定位氢原子以及随后的能量和成键分析，但XWR提供了这样做的理想能力，从而回答了开放的问题。在第二部分，XWR将扩展到材料科学。许多技术感兴趣的材料是扩展固体，即不适合分子波函数的周期化合物。此外，它们不能形成足够大的单晶来进行常规的X射线结构测定，即只有粉末衍射是可行的。因此，我们将利用极端定域分子轨道和产生极端定域Wannier函数的Wannier函数的技术来发展周期性的XWR。此外，我们将开发一种迭代的XWR-Rietveld精化方法，该方法可以从粉末样品中进行改进的结构确定。通过这两种新开发方法的结合，将XWR应用于扩展固体粉末将是可能的。这将首次允许在亚原子水平上从实验上研究粉末的材料特性，重点放在成键方面。我们将从研究Skutterudite类材料的热电性质和莫来石类材料的热致变色性质开始。

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.