Conceptual density functional theory.

It is an understatement to say that the density functional theory (DFT) has strongly influenced the evolution of quantum chemistry during the past 15 years; the term “revolutionalized” is perhaps more appropriate. Based on the famous Hohenberg and Kohn theorems,1 DFT provided a sound basis for the development of computational strategies for obtaining information about the energetics, structure, and properties of (atoms and) molecules at much lower costs than traditional ab initio wave function techniques. Evidence “par excellence” is the publication of Koch and Holthausen’s book, Chemist’s Guide to Density Functional Theory,2 in 2000, offering an overview of the performance of DFT in the computation of a variety of molecular properties as a guide for the practicing, not necessarily quantum, chemist. In this sense, DFT played a decisive role in the evolution of quantum chemistry from a highly specialized domain, concentrating, “faute de mieux”, on small systems, to part of a toolbox to which also different types of spectroscopy belong today, for use by the practicing organic chemist, inorganic chemist, materials chemist, and biochemist, thus serving a much broader scientific community. The award of the Nobel Prize for Chemistry in 1998 to one, if not the protagonist of (ab initio) wave function quantum chemistry, Professor J. A. Pople,3 and the founding father of DFT, Professor Walter Kohn,4 is the highest recognition of both the impact of quantum chemistry in present-day chemical research and the role played by DFT in this evolution. When looking at the “story of DFT”, the basic idea that the electron density, F(r), at each point r determines the ground-state properties of an atomic, molecular, ... system goes back to the early work of * Corresponding author (telephone +32.2.629.33.14; fax +32.2.629. 33.17; E-mail [email protected]). † Vrije Universiteit Brussel. ‡ Janssen Pharmaceutica NV. 1793 Chem. Rev. 2003, 103, 1793−1873