Chair of Solid-State and Quantum Chemistry
Welcome to the Chair of Solid-State and Quantum Chemistry at RWTH Aachen University, Europe's largest Technical University dating back to the year 1870. The following pages are intended to offer you a short overview of our research and teaching activities in the fields of solid-state and quantum chemistry. If you are interested in these exciting chemical disciplines, you have come to the right place. Stay with us! Don't go away!
HOT: Chemical Bonding in Phase-Change Materials
Almost all phase-change memory materials (PCM) contain chalcogen atoms, and their chemical bonds have been denoted both as 'electron-deficient' [sometimes referred to as 'metavalent'] and 'electron-rich' ['hypervalent', multicentre]. The latter involve lone-pair electrons. We have performed calculations that can discriminate unambiguously between these two classes of bond and have shown that PCM have electron-rich, 3c–4e ('hypervalent') bonds. Plots of charge transferred between (ET) and shared with (ES) neighbouring atoms cannot on their own distinguish between 'metavalent' and 'hypervalent' bonds, both of which involve single-electron bonds. PCM do not exhibit 'metavalent' bonding and are not electron-deficient; the bonding is electron-rich of the 'hypervalent' or multicentre type.
DOI:10.1088/1361-648X/ad46d6
HOT: Neutron Diffraction: a Primer
Because of the neutron's special properties, neutron diffraction may be considered one of the most powerful techniques for structure determination of crystalline and related matter. Neutrons can be released from nuclear fission, from spallation processes, and also from low-energy nuclear reactions, and they can then be used in powder, time-of-flight, texture, single crystal, and other techniques. With high neutron flux and sufficient brilliance, neutron diffraction also excels for diffuse scattering, for in situ and operando studies as well as for high-pressure experiments of today's materials. For these, the wave-like neutron's infinite advantage (isotope specific, magnetic) is crucial to answering important scientific questions, for example, on the structure and dynamics of light atoms in energy conversion and storage materials, magnetic matter, or protein structures. We summarize the current state of neutron diffraction (and how it came to be), but also look at recent advances and new ideas, e.g., the design of new instruments, and what follows from that.
DOI:10.1515/zkri-2024-0001
HOT: The Carbodiimide Complex Anion and Its Compounds
Synthetic strategies guided by quantum chemistry eventually leading to inorganic nitridocarbonates containing the NCN2– complex carbodiimide anion are presented, showing the power of rational approaches in obtaining chemically tailored carbodiimides with exciting materials properties. In addition, we showcase various exemplary compounds and their attributes containing either the carbodiimide [N=C=N]2– or the cyanamide [N≡C–N]2– anion. Infrared, Raman, NMR, Mößbauer and other spectroscopies, in addition to density-functional theory, are discussed, and we also highlight future perspectives of carbodiimide chemistry by focusing on their magnetic, catalytic, and electrochemical behavior, a consequence of their oxide-analogous but more covalent bonding.
DOI:10.1021/acs.chemmater.4c01615
Solid-State Chemistry
Here's the message: We honestly believe that solid-state chemistry is one of the most exciting chemical disciplines. This fundamental brand of the chemical sciences brings us into contact with a large part of the "real world" surrounding us, and a creative solid-state chemist is in true command of the entire periodic table when he or she decides to make new compounds with often unforeseeable but exciting physical properties. Solid-state chemistry is truly interdisciplinary and borders with solid-state physics, crystallography, quantum theory, metal science, and inorganic chemistry, to name but a few; also, it is one of the rock-solid platforms on which the increasingly popular fields of nanoscience and nanomaterials may be built.
Some of the breathtaking technological advances of the 20th, and also the early 21st century, would have been totally impossible without the fundamental research originating within solid-state chemistry, for example cleverly designed insulators such as dielectric ceramics for data transmission, novel ionic conductors for energy storage in hand-held electrical devices, magnetic intermetallics and oxides for data storage applications, advanced nitrides for electro-optical and diverse mechanical purposes, and also superconductors for energy transport and communication applications. In addition, there is also curiosity-driven research in solid-state chemistry, touching upon chemical systems you probably have never heard of. Interested? Read more about our research to become addicted...
Teaching
 No research today? The teaching section is intended to inform chemistry (and other) students about the various chemistry courses offered by this chair at the Institute of Inorganic Chemistry.
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Computational Chemistry
Computational chemistry is an ingenious, non-experimental way to solve chemical problems by means of sheer computation on the basis of hard-core numerical methods (which are typically quantum-chemical in nature), and this approach has become an increasingly important part of the chemical sciences. Our group specializes in the quantum chemistry of solids (well, that's not too surprising) and we surely know how to solve Schrödinger's equation for periodic systems. In fact, there has been huge progress in properly describing the whole universe of solid-state materials (insulators, semiconductors, metals, and intermetallic compounds) by electronic-structure theory; in addition, predictive conclusions are now in our own hands.
While the numerical methods of ours include very different quantum-chemical tools, their varying levels of accuracy and speed are due to differences in the atomic potentials and the choice of the basis sets involved. The latter may either be totally delocalized (plane waves) or localized (atomic-like), adapted to the valence electrons only (pseudopotentials) or to all the electrons. In order to understand structures and compositions, the results of electronic-structure theory are investigated in terms of further quantum-chemical bonding analyses. There are also cases where one would like to know more about the dynamical behavior of the various atoms, and then the time evolution of their spatial coordinates (that is, their "trajectories") must be calculated as a function of the macroscopic temperature, for example by molecular-dynamics approaches. Go to our research section to learn more about theory and computation. It's fun!
Location
 Although the history of Aachen reaches back to Roman times about 2,000 (and more) years ago, RWTH Aachen University is relatively young for European (not American) standards since it was founded at the end of the 19th century, at the peak of the industrial revolution. Today, RWTH Aachen University is Europe's largest technical university with very famous engineering schools, and its national as well as international reputation also goes back, in part, to its chemistry division. Find out more about our location and our laboratories. If you come from outer space, you may prefer to have a look at our institute from the sky using Google Earth (see top of page).
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