ABSTRACT
Chemical reactivity is the best success story of density functional theory (DFT). In a recent article, Geerlings and De Proft provide an extensive description of the successful pathway of DFT [1]. The step from quantum mechanics into what quantum chemistry can, in principle, be situated in the pioneering work by Heitler and London [2] on hydrogen molecules in 1927, which endows with the insight into the nature of the chemical bond [3]. In the years between 1930 and 1950, Pauling [3], Huckel [4], and Coulson [5] combined quantum mechanical principles with their chemical intuition to create a new discipline, called quantum chemistry. The valence bond approach (after Heitler and London) was prominent in those days, to the detriment of Hund’s and Mulliken’s molecular orbital (MO) method [6]. A revolution was provoked by Roothaan’s matrix formulation of the MO method in 1951 [7]. Its elegance together with the increasing computer power paved the way for the large-scale introduction of the molecular orbital-lineal combination of atomic orbital (MO-LCAO) method within the framework of the Hartree Fock self-consistent field (SCF) approach as detailed in Pople’s comprehensive treatise [8]. The late 1970s, 1980s, and 1990s saw the development and/or the adaptation for systematic use of methods beyond SCF including electron correlation: Møller Plesset perturbation theory [9], the method of configuration interaction [10], and various types of coupled cluster theory [11]. The introduction of initially freely distributed, later on commercially available, computer programs that became increasingly user friendly (Pople et al.’s Gaussian series) [12], Delley’s DMol3 [13], and Payne’s CASTEP [14]) definitely promoted quantum chemistry, from a branch of theoretical chemistry almost exclusively reserved for “pure-sang” theoreticians and concentrating on diatomic and small polyatomic molecules, to a field also creating tools for nonspecialists, in many other subfields of chemistry (inorganic, organic, biochemistry).
