Quantum chemistry in the 21st century (Special topic article)

Abstract

Quantum chemistry is the field in which solutions to the Schrödinger equation are used to predict the properties of molecules and solve chemical problems. This paper considers possible future research directions in light of the discipline's past successes. After decades of incremental development—accompanied by a healthy dose of skepticism from the experimental community—the ready availability of fast computers has ushered in a "golden age" of quantum chemistry. In this new era of acceptance, theoretical predictions often precede experiment in small molecule chemistry, and quantum chemical methods play an ever greater role in biochemical and other larger systems. Quantum chemists increasingly divide their efforts along three fronts: high-level (spectroscopic) accuracy for small molecules, characterized by such techniques as Brueckner methods, r12 formalisms, and multireference calculations; parameterization- or extrapolation-based intermediate-level schemes (such as Gaussian-N theory) for medium molecules; and lower-level (chemical) accuracy for large molecules, characterized by density functional theory and linear scaling techniques. These tools, and quantum chemistry as a whole, are examined here from a historical perspective and with a view toward their future applications.