Quantum chemistry, also known as molecular quantum mechanics, is a branch of physical chemistry that applies the principles of quantum mechanics to understand and predict the electronic properties, structures, and behaviors of molecules, materials, and solutions at the atomic level. It employs various computational methods, often utilizing the Born-Oppenheimer approximation, to study electronic ground and excited states, reaction pathways, and to predict spectroscopic data. A central goal is to computationally solve the Schrödinger equation, though the field continually strives to increase the accuracy for small systems and expand the computational feasibility for larger molecules.
Historically, Gilbert N. Lewis provided a critical conceptual framework with his 1916 paper on valence electrons. However, the true birth of quantum chemistry is often attributed to Walter Heitler and Fritz London's 1927 article, which first applied quantum mechanics to describe the chemical bond in the diatomic hydrogen molecule. Linus Pauling's seminal 1939 text, "The Nature of the Chemical Bond," integrated earlier work and widely popularized the field, establishing valence bond theory as a foundational framework for chemists.