The development of exchange and correlation functionals that also included the gradient (GGA functionals) and second derivatives (meta-GGA functionals) of the electron density permitted more accurate calculations. The simplest exchange and correlation functionals depend only on the electron density itself. Exchange and correlation functionals are used to approximate the difference to the real system. KohnвЂ“Sham DFT calculates the energy of a non-interacting reference system. The simplifications of the HartreeвЂ“Fock method by Slater has enabled practical DFT calculations. Thomas and Fermi proposed the very first density functional approximation without mentioning the term. Besides the foundational theorems by Hohenberg and Kohn, DFT stands on many other pillars. KohnвЂ“Sham DFT has become one of the most important methods to solve the SchrГ¶dinger and Dirac equations approximately. In this paper, we were able to use a very large data set as the basis for our analysis to cover the complete research field of density functional theory (DFT) and its applications from a chemical perspective. An overview of further studies based on RPYS can be found in Marx and Bornmann.

Very large publication sets can be analyzed by sampling methods implemented in the CRExplorer. For example, RPYS analyses have been performed to discover the historical roots of individuals, publications in a journal, or research fields. Therefore, RPYS results often provide a different perspective or complement the individual expertвЂ™s perspective on the field. RPYS, however, can answer this question in an objective way by asking all researchers in the field (via the cited references in their publications) with subsequent quantitative analysis. The question about seminal papers in a given field can be answered by researchers in the field only in a subjective way. This bibliometric method can be used to locate seminal papers which are cited most frequently in a certain publication set. One approach of such an analysis is called reference publication year spectroscopy (RPYS). In this study, we turn the perspective backwards from the individual publication and analyze the cited references (i.e., the number of times a specific reference is included in the reference lists). The perspective of research evaluation looks forward in time from the individual publication and the corresponding citing papers are counted. They are used to construct bibliometric indicators for research evaluation purposes. The most basic quantities used in bibliometrics are publication and citation counts. The terms bibliometrics or scientometrics (in a broader sense) are often used synonymously and can be characterized as the discipline that provides a quantitative overview about science. Perdew and co-workers, and Georg Kresse and co-workers. Exceptions are 19 due to seminal papers by Axel Becke, John P.

Since the 1990s, only very few pronounced peaks occur as most years were referenced nearly equally often. The foundational papers of DFT by Hohenberg and Kohn as well as Kohn and Sham do not seem to be affected by obliteration by incorporation as they appear as pronounced peaks in our RPYS analysis. The references to papers published in the 19th century mainly served the purpose of referring to long-known physical and chemical phenomena which were used to test if DFT approximations deliver correct results (e.g., Van der Waals interactions). The earliest cited reference we found was published in 1806.

(iii) Finally, various very frequently employed DFT approximations, basis sets, and other techniques (e.g., implicit descriptions of solvents) constitute another group of seminal papers. (ii) Fundamental quantum-chemical papers from the time period 1900вЂ“1950 which predate DFT form another group of seminal papers. The RPYS analysis revealed three different groups of seminal papers which researchers in DFT have drawn from: (i) some long-known experimental studies from the 19th century about physical and chemical phenomena were referenced rather frequently in contemporary DFT publications. 114,138 publications with their 4,412,152 non-distinct cited references are analyzed. This bibliometric study aims at providing a comprehensive analysis of the history of density functional theory (DFT) from a perspective of chemistry by using reference publication year spectroscopy (RPYS).

Amsterdam density functional