Quantum chemical calculations are widely used to understand the structure, reaction mechanisms, and electronic properties of molecules and solids, and have become an essential research method in modern chemistry. Inspired by his experimental studies of conducting polymers, magnetic molecules, and fullerenes as a student, as well as developmental studies in industry, Dr. Kazunari Yoshizawa has been conducting a wide range of theoretical research based on quantum chemical calculations. His research interests include the selective oxidation of methane, analysis and design of nitrogen fixation reactions by transition-metal complexes, frontier orbital theory of single molecule conduction, molecular understanding of adhesive interface interactions, and many other topics. He has also conducted many collaborative studies with experimental researchers in the fields of coordination chemistry, organometallic chemistry, catalytic chemistry, and polymer chemistry. His major achievements are listed below.

1. Theoretical study on the selective oxidation process of methane
He has been working on the structure and reaction of metalloenzymes and metal- complex catalysts using quantum chemical calculations such as the extended Hückel method, density functional theory, and the so-called QM/MM method, which combines quantum mechanics and molecular mechanics. Since 2010, he has shifted his research focus to complex chemical systems, including heterogeneous catalysts, which electronic structure theory has not been good at. For example, in the selective oxidation of methane, his group has conducted theoretical studies using first-principles calculations on reactions with metal zeolites and reactions on metal oxide surfaces. In the study of methane activation on oxide surfaces, orbital interactions between methane and IrO₂(110) surface were analyzed, and design guidelines for methane activation catalysts were obtained. From this guideline, they predicted that the β-PtO₂(110) surface would show stronger activity, and this prediction was later verified experimentally in a collaborative study with Takagaki et al. of Yokohama National University. Furthermore, the reactivity of two-component alloy surfaces was predicted for the C-H bond activation of methane and the formation of C₂ species such as ethane and ethylene by exhaustive first-principles calculations and catalytic informatics. By controlling the potential energy surface, MgPt alloy was selected as a promising alloy to produce C₂ species, and this theoretical prediction was successfully verified in cooperation with Abe et al. of NIMS and Yamanaka et al. of Tokyo Institute of Technology.

2. Collaborative theoretical and experimental research on catalytic nitrogen fixation reactions
A distinctive feature of his theoretical research is the extensive collaboration with experimental researchers. First, his group conducted theoretical research on nitrogen-trapping Cubane-type complexes based on quantum chemical calculations with Mizobe et al. of the University of Tokyo, and obtained the theoretical inspiration for nitrogen fixation by metal complexes. His group has conducted a collaborative experimental and theoretical study on nitrogen-fixing complex catalysts with Nishibayashi et al. of the University of Tokyo, and has realized catalytic ammonia conversion reactions. The close collaboration between experiment and theory has led to a deeper understanding of the reaction mechanism and improved catalytic performance, and they have succeeded in developing nitrogen-fixing complex catalysts with several thousand catalytic revolutions. Thus, in addition to his theoretical work contributing to the development of nitrogen fixation, he has developed extensive collaborations with experimentalists in complex chemistry, organometallic chemistry, and catalytic chemistry in the last decade.

3. Frontier orbital theory of single molecule conduction
The control of single molecule electrical conduction is a key to the development of nanotechnology. Based on the Green's function method and the Hückel molecular orbital method, his group has found that the electron transport in a molecule is determined by the phase and amplitude of the HOMO and LUMO of the molecule. Based on this orbital theory, his group theoretically predicted that there exist pathways through which electrons can pass easily and pathways through which electrons cannot pass easily in a molecule. For example, when electrodes are connected to the 1- and 4-positions of naphthalene, large electron transport is obtained. On the other hand, when the 2- and 7-positions are connected, the electron transport is extremely small. This theoretical prediction was experimentally verified by the organic synthesis of Sugawara et al. of the University of Tokyo and the single molecule conduction measurements by the break junction method of Taniguchi et al. of Osaka University. This is one of the few examples of theory-driven research in chemistry for complex systems.

4. Molecular understanding of adhesive-interface interactions
Dr. Yoshizawa was involved in research on corrosion protection technology for steel materials at a company, and has experience in development research on adhesion between metals and polymers. Inspired by this research, he has been conducting world-leading theoretical research on adhesion. Although adhesive-interface interactions are one of the most fundamental research topics in surface science, there has been no serious theoretical study on how adhesion is caused by interfacial interactions. His group has been working on the elucidation of adhesion phenomena by first-principles calculations, and has developed a theoretical study of the adhesive interface interaction between epoxy resin and surfaces such as aluminum, gold, copper, glass, carbon, boron nitride, and so on. First, his group proposed a method for estimating adhesive forces from first-principles calculations and succeeded in performing a detailed analysis of the adhesive interactions by dividing them into four components: electrostatic interaction, exchange repulsion, charge transfer, and dispersion force, using the energy-decomposition analysis. Quantum chemical calculations show that electrostatic interactions and dispersion forces are important contributors to the strong adhesion of hydrophilic surfaces, whereas only dispersion forces are mainly responsible for hydrophobic surfaces. His group also discusses the effect of adsorbed water on adhesion. His research on adhesive-interfacial interactions ushered in a new research area that could be called the "molecular theory of adhesion.

As described above, Dr. Yoshizawa has conducted original research on the theoretical study of methane activation, the experimental and theoretical studies on the catalytic nitrogen fixation reactions, the frontier orbital theory of single molecule conduction, and the molecular interpretation of adhesive-interface interactions, etc., by widely applying quantum chemical calculations. He has achieved numerous results in the elucidation of complex chemical phenomena governing chemical reactions and electronic properties, as well as in theoretical research that in some cases leads experiments. Therefore, his achievements are recognized as worthy of the Chemical Society of Japan Award.