Overview of the complex but fruitful relationship between molecular chemistry and quantum mechanics, in celebration of the Year of Quantum Sciences and Technologies.
The United Nations General Assembly has officially designated 2025 as the International Year of Quantum Science and Technology (IYQ). This global initiative, supported by UNESCO and co-sponsored by several countries, marks the centenary of quantum sciences, which encompass quantum mechanics, quantum chemistry, and related fields. These disciplines serve as the foundation for fundamental research across the natural sciences. Quantum mechanics provides the theoretical framework for understanding matter and energy at the microscopic scale. While public celebrations of the International Year of Quantum Science and Technology often showcase quantum technologies to engage a broader audience, it is crucial to remember that the emergence of quantum theory primarily represented a ground-breaking shift in the basic sciences. This article explores the complex relationship between quantum mechanics and concepts of traditional chemistry, particularly concerning the microscopic world of atoms and molecules. It highlights how quantum mechanics, a holistic and nonlocal theory, features concepts such as entanglement and the indistinguishability of components that challenge classical chemical notions of distinct interatomic interactions and well-defined molecular structures. While quantum mechanics excels at determining the overall stability and dynamics of the system, the article explains that quantum chemistry relies on the classical Born-Oppenheimer approximation to maintain the view of local interactions and identifiable atoms within a molecule. Then, the article discusses the historical development and limitations of transition state theory in explaining chemical reactions, highlighting chemistry’s specific focus on bond breaking and bond making as a fundamental explanatory principle.
The United Nations General Assembly has officially designated 2025 as the International Year of Quantum Science and Technology (IYQ). This global initiative, supported by UNESCO and co-sponsored by several countries, marks the centenary of quantum sciences, which encompass quantum mechanics, quantum chemistry, and related fields. These disciplines serve as the foundation for fundamental research across the natural sciences. Quantum mechanics provides the theoretical framework for understanding matter and energy at the microscopic scale. While public celebrations of the International Year of Quantum Science and Technology often showcase quantum technologies to engage a broader audience, it is crucial to remember that the emergence of quantum theory primarily represented a ground-breaking shift in the basic sciences. This article explores the complex relationship between quantum mechanics and concepts of traditional chemistry, particularly concerning the microscopic world of atoms and molecules. It highlights how quantum mechanics, a holistic and nonlocal theory, features concepts such as entanglement and the indistinguishability of components that challenge classical chemical notions of distinct interatomic interactions and well-defined molecular structures. While quantum mechanics excels at determining the overall stability and dynamics of the system, the article explains that quantum chemistry relies on the classical Born-Oppenheimer approximation to maintain the view of local interactions and identifiable atoms within a molecule. Then, the article discusses the historical development and limitations of transition state theory in explaining chemical reactions, highlighting chemistry’s specific focus on bond breaking and bond making as a fundamental explanatory principle.
This introductory chapter provides an overview of quantum mechanics, which is a subject of central importance in chemistry, and is by nature a mathematical theory. The chemist's approach to the understanding of matter and its chemical transformations is to take a microscopic view, connecting experimental observation with the properties of constituent molecules. However, at the microscopic level, atoms, molecules, and their constituent particles do not obey the familiar laws of mechanics that pertain to the everyday macroscopic world. For example, the existence of molecular line spectra indicates that molecules can be found only at certain well-defined energies, unlike objects at our own scale whose energy appears to be continuously variable. This book aims to explain the fundamentals of quantum mechanics from the point of view of chemistry; describe the areas of chemistry where quantum mechanics is most important; and show how quantum mechanics is applied to chemical problems.
Abstract 2025 was proclaimed by the United Nations proclaimed the International Year of Quantum Science and Technology (IYQ). This year-long and worldwide initiative aims at increasing public awareness of the importance of quantum science and applications. As the world authority on chemical nomenclature and terminology, standardized methods for measurement, atomic weights and many other critically evaluated data, IUPAC is naturally a supporter. Compiled under the leadership of Russell Boyd and Manuel Yáñez acting as co-editors, a special issue of IUPAC journal Pure and Applied Chemistry (PAC) is dedicated to the celebration of IYQ.
Abstract Chemistry is about the atom and molecule, motion of which follows quantum mechanics established 100 years ago by Werner Heisenberg, inspired by a number of milestone findings including Max Planck’s first quanta concept for black body radiation, Albert Einstein’s photon concept for photoelectric effect and oscillator quanta for heat capacity of solid, and Niels Bohr’s quantum model for atomic structure. Independently, inspired by Louis de Broglie’s particle-wave duality, Erwin Schrödinger established wave mechanics, which is shown to be equivalent to Heisenberg’s mechanics by Paul Dirac. The latter further established the relativistic quantum mechanics, and then claimed that the underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws lead to equations much too complicated to be soluble. In the occasion of celebrating The International Year of Quantum Science and Technology (IYQ 2025, quantum2025.org), we will present a heuristic review of the development of quantum theory and its application to chemistry, namely, quantum chemistry (QC). Then, we will discuss some of the current challenges and the future developments, especially on the quantum computing for quantum chemistry (QCQC).
Quantum science underpins many of the most significant advances in modern physics, chemistry, and information technology. Quantum physics provides the fundamental laws governing matter and energy at microscopic scales, quantum chemistry applies these principles to explain molecular structure, bonding, and reactivity, and quantum computing seeks to exploit quantum phenomena such as superposition and entanglement to enable new computational paradigms. Despite their long-standing theoretical foundations and experimental successes, all three domains remain surrounded by persistent misconceptions, often amplified by abstract formalisms, popular science narratives, and rapid technological developments. This contemporary review critically examines the established facts and common myths associated with quantum physics, quantum chemistry, and quantum computing. Emphasis is placed on experimentally verified principles, computational feasibility, and realistic assessments of current capabilities. Recent advances reported between 2020 and 2025 are reviewed to highlight genuine progress in areas such as quantum simulations, molecular modeling, and noisy intermediate-scale quantum (NISQ) devices, while also addressing their practical limitations. By distinguishing validated achievements from speculative claims, this review provides a balanced, evidence-based perspective on modern quantum science. The article aims to clarify enduring misconceptions, promote conceptual clarity across disciplines, and outline realistic future directions for research and applications in quantum technologies.
2025 is the year UNESCO selected to celebrate 100 years of this novel science, quantum mechanics, based on Heisenberg’s “uncertainty principle” discovery. However, quantum mechanics began with the discovery of quantum packets of energy emission formulated by the German physicist Max Planck, and it incorporated additional discoveries and principles from Albert Einstein, Niels Bohr, Heisenberg, Pauli, de Broglie, and many others in the early 1900s. Since then, many advancements and breakthroughs have been made. Such scientific contributions have influenced the culture and technology of humanity from the 20th century onwards, with the first quantum revolutions bringing innovations in technology and engineering, including the omnipresent light amplification by stimulated emission of radiation (Laser), magnetic resonance imaging (MRI), microprocessor manufacturing and design for computers and nuclear energy. Thus, at the beginning of the Second Quantum Revolution in the 21st century, amid a new wave of novel quantum technologies promising to create the 5th Industrial Revolution and transform humanity, a brief history of these marvellous sciences is condensed, connecting the wonders of the new quantum technogenesis that is being forged, linking its past with classical mechanics and also with novel relativistic mechanics. Understanding these developments highlights the significance of quantum technologies shaping our future and what lies ahead for us. This article explores technologies that are presently under research and development (R&D) in the quantum physics realm, including quantum computing, quantum cryptography, quantum sensing and metrology, and quantum simulation. It also discusses emerging careers in the quantum field and the unresolved mysteries that continue to challenge scientists. The discussion follows the ancient griot tradition of storytelling, a method that the distinguished physicist, great professor, and Nobel laureate Richard Feynman encouraged us to use to explain complex scientific ideas.
Over the past years, the development of experimental techniques for the coherent manipulation and control of isolated quantum systems has made impressive progress. Such 'quantum-logic' methods are also highly attractive in a chemical context in view of unravelling and controlling the quantum dynamics of molecular collisions and chemical reactions. Quantum technologies have the potential to transform the way chemical dynamics are investigated - by providing highly sensitive methods for state readout and spectroscopy, by opening up new pathways for the quantum-state preparation of molecules and by enabling an improved control of their microscopic behavior on the single-particle level. However, for complex quantum systems like molecules, these techniques are still in their infancy and their considerable potential remains to be unlocked. The aim of the present research program supported by an Advanced Grant of the Swiss National Science Foundation is to merge the fields of quantum science and chemical dynamics by advancing quantum technologies to polyatomic molecular ions and by applying them to the study of ion-molecule collisions and chemical reactions. In this article, we review the salient experimental methods as well as prospects and challenges in the development of molecular quantum technologies and their applications to chemistry.