Perspective on “The physical nature of the chemical bond”

Abstract

“I believe that a good theory combines mathematical rigor with physical interpretation.” With these words, Klaus Ruedenberg began a summary of the highlights of his scientific career in 1996. Many seminal papers by this giant in the field of quantum chemistry serve to illustrate this philosophy; none accomplish the task with more beauty and insight than “The physical nature of the chemical bond” [1]. This paper and those that followed it [2-4] represent the first rigorous, first-principles analysis of the fundamental quantum mechanical origins of covalent bonding which, as Mulliken [5] noted in 1977, “are commonly misunderstood”. With the insight that has become his trademark, Ruedenberg combined four fundamental precepts — the virial theorem, wave—particle duality, the variational principle and the decomposition of the total energy into kinetic and potential components — to devise a model that is both simple and broadly applicable. This paper clearly establishes the important point that it is “possible to extract from a rigorous wavefunction (or a bonafide approximation to it), in a quantitative fashion, a partitioning of the energy which justifies conceptual interpretations.”