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Have you ever heard of nonadiabatic chemical reactions? These are reactions that involve transitions between different electronic states. Such transitions can alter the electronic, magnetic, and chemical properties of molecules and materials, opening reaction pathways that are inaccessible on a single electronic state.
Nonadiabatic processes are particularly important in transition-metal systems, where multiple electronic states often lie close in energy. The presence of accessible oxidation and spin states allows electron transfer, spin-state transitions, and changes in chemical bonding to become strongly coupled during a reaction.
Nature exploits this electronic flexibility in metalloproteins to carry out processes such as electron transfer, bond activation, and energy conversion. Chemists likewise exploit transition-metal complexes, catalysts, and transition-metal oxides to promote a wide range of chemical transformations. Understanding these processes can therefore provide fundamental insight into chemical reactivity and guide the design of new molecules and materials.
Because nonadiabatic reactions involve multiple electronic states, they are inherently quantum mechanical and often difficult to understand through conventional chemical intuition. Revealing their mechanisms therefore requires close interplay between theory and experiment.
Development of Electronic-Structure Theory for Transition-Metal Molecules and Materials
Electronic-structure theory is a central theoretical tool for understanding the electronic and magnetic properties of molecules and materials. Over the past several decades, quantum chemists have developed a wide range of computational methods capable of describing chemical systems with remarkable accuracy. Despite this progress, accurate electronic-structure simulations remain challenging for systems with strong electron correlation, particularly those involving transition metals, as well as for large and complex systems such as proteins and extended materials.
Our research group uses computational simulations to investigate important nonadiabatic chemical processes in transition-metal-containing molecules and materials. To make such simulations both accurate and practical, we develop efficient and systematically verifiable quantum-chemical methods that can reliably describe changes in electronic structure and electronic state throughout these processes.
Nonadiabatic processes in metalloenzymes
Approximately 40% of enzymes are known to contain metal ions, and in many cases, transition-metal centers serve as the active sites responsible for catalytic function. Understanding the role of these metal centers—and the factors that enable efficient catalysis—can provide important guiding principles for the development of new catalysts.
What insights can quantum-chemical electronic-structure theory provide into these catalytic processes, and what challenges must be overcome to describe them accurately?
Learn More →Nonadiabatic processes in transition-metal oxides/sulfides
Transition-metal oxides can exhibit dramatic changes in their electronic and magnetic properties in response to changes in their surrounding environment, making them highly versatile functional materials. They play important roles in a wide range of scientific and technological applications, including battery cathodes, solar cells, high-temperature superconductors, and catalysis.
Applying quantum-chemical methods to these materials can provide microscopic insight into how changes in structure, composition, and external conditions give rise to changes in their physical and chemical properties. What makes accurate theoretical simulation of these systems so challenging, and how can we overcome these limitations?
Learn More →Electronic structure of transition-metal clusters
Molecules containing two or more interconnected transition-metal centers are known as transition-metal clusters. Such clusters are found at the active sites of several metalloenzymes, where they enable remarkably challenging chemical transformations, including the conversion of carbon monoxide to hydrocarbons, nitrogen to ammonia, and water to molecular oxygen.
Computational chemists seek to understand these reactions through quantum-chemical simulations. However, even determining the ground-state electronic structure of a transition-metal cluster can be one of the most challenging problems in electronic-structure theory because of the strong interactions among multiple metal centers and their electrons. What theoretical approaches can overcome these challenges and provide reliable descriptions of their chemistry?
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