The influence of quantum theory on chemistry

Abstract An overview is given of the most important contributions to the development of quantum chemistry since the first paper by Heitler and London in 1927. In this pioneering work it was shown that the physical nature of chemical bonding is a quantum theoretical phenomenon that can only be understood on the basis of the quantum theory presented by Heisenberg and Schrödinger in 1925/1926. The direct influence on chemistry was minimal at the beginning, and it was initially physicists who solved problems in chemistry. These were among others the triplet state of O 2 by Lennard-Jones, the aromatic stability of benzene by Erich Hückel and the energy contributions of chemical bonding by Hellmann, who wrote the first book on quantum chemistry in 1936. The importance of quantum theory for chemistry was recognized by Linus Pauling, who succeeded in translating the complicated mathematical representation into simple models that were useful for many areas of chemistry. His book “The Nature of the Chemical Bond” was the first to bridge the gap between quantum theory and the broad field of chemical research. With the introduction of computers, quantum chemistry has undergone continuous development, from which it still benefits today. The Valence Bond theory favored by Pauling was largely replaced by the Molecular Orbital theory, as the computer calculations are much faster and the symmetry of the wave function contains fundamental information that can be used to explain the structure and reactivity of molecules. Orbital symmetry forms the basis of the most important models in chemistry, on which the frontier orbitals of Fukui and the orbital symmetry of Woodward and Hoffmann are based. Parallel to the development of the hardware, the methodological foundations and programs were developed with which practically all molecular properties can be calculated. In the 2000s, molecular orbital methods were replaced by density functional methods as the most widely used tool of computational chemistry.