Deepening and Extending the Quantum Principles in Chemistry

Abstract

A brief summary of the author's research projects for deepening and extending the quantum principles in chemistry is given. First, the structure of the exact wave function that is the solution of the Schrödinger equation was clarified and a method of calculating it starting from an approximate wave function is given. The singularity problem intrinsic to atoms and molecules was overcome, and a general method of solving the Schrödinger equation in an analytical form has been established. Quantum chemistry of excited states and ionized states is essential since it is difficult with experiments alone to explore this field due to the short lives of these species. The SAC-CI theory developed in the author's groups offers a powerful method for investigating the chemistry of excited and ionized states. The energy gradient method incorporated into this program is particularly useful for studying geometries and reactions involving these states. The catalysis on a metal surface is a magic process that must be clarified with the help of quantum theory. The author studied it using his dipped adcluster model (DAM) that includes the effects of the free electrons of the bulk metal. The epoxidation reactions of ethylene and propylene were studied with this method. The NMR chemical shifts include much information about the valence electrons of molecular systems. The author clarified that the major electronic mechanisms of the chemical shifts could be attributed to the intrinsic atomic properties that are related to the position of the element in the periodic table.For the chemical shifts induced by heavy ligands, the relativistic effect is sometimes dominant. The spin-orbit effect is most important for light resonant nuclei. For heavier resonant nuclei, other spin-free relativistic effects and the electron correlation effects are also important and they strongly couple with each other, implying an existence of something ''unexpected'' in the chemistry of heavy elements. Finally, the strategy of the author's study in quantum chemistry is shortly described.

Full configuration-interaction calculations with the simplest iterative complement method: Merit of the inverse Hamiltonian

“…The SSE has led to several general ways of solving the SE, among which we have used the free complement (FC) method [5,6] most frequently [17] to solve the SE of atoms and molecules.…”

QM/MM method for metal–organic interfaces

“…These include the Green function method, based on a continuum model for the classical region, [59][60][61] and the dipped ad-cluster model, which is most suitable for studying chemisorption and surface reactions that involve electron transfer between the molecules and the metal. [62][63][64] Extensions of the latter model include the treatment of the image forces arising from charge transfer.…”

Left‐eigenstate completely renormalized equation‐of‐motion coupled‐cluster methods: Review of key concepts, extension to excited states of open‐shell systems, and comparison with electron‐attached and ionized approaches

“…Ref. 67 for an overview of the relevant mathematical concepts), or their EA and IP counterparts 142, 151–156 based on the more general SAC‐CI framework 151–163. In these methods, one obtains the electronic states of radicals by applying the electron attaching or ionizing operator R with the 1‐particle (1 p ) or 1‐hole (1 h ), 2‐particle–1‐hole (2 p ‐1 h ) or 2‐hole–1‐particle (2 h ‐1 p ), etc.…”