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WikiHarold moved page Chemistry:Quantum chemistry to Physics:Quantum chemistry without leaving a redirect

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2026-05-04T10:54:06Z

WikiHarold moved page Chemistry:Quantum chemistry to Physics:Quantum chemistry without leaving a redirect

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'''Quantum chemistry''', also called '''molecular quantum mechanics''', is a branch of [[Chemistry:Physical chemistry|physical chemistry]] focused on the application of [[Physics:Quantum mechanics|quantum mechanics]] to chemical systems, particularly towards the quantum-mechanical calculation of electronic contributions to physical and chemical properties of [[Physics:Molecule|molecules]], [[Physics:Material|materials]], and solutions at the atomic level.<ref>{{Cite book |last=McQuarrie |first=Donald A. |title=Quantum Chemistry |publisher=University Science Books |year=2007 |isbn=978-1891389504 |edition=2nd}}</ref> These calculations include systematically applied approximations intended to make calculations computationally feasible while still capturing as much information about important contributions to the computed [[Wave function|wave functions]] as well as to observable properties such as structures, spectra, and thermodynamic properties. Quantum chemistry is also concerned with the computation of quantum effects on [[Physics:Molecular dynamics|molecular dynamics]] and [[Chemistry:Chemical kinetics|chemical kinetics]].

Chemists rely heavily on [[Physics:Spectroscopy|spectroscopy]] through which information regarding the [[Physics:Quantization|quantization]] of energy on a molecular scale can be obtained. Common methods are infra-red (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and [[Physics:Scanning probe microscopy|scanning probe microscopy]]. Quantum chemistry may be applied to the prediction and verification of spectroscopic data as well as other experimental data.

Many quantum chemistry studies are focused on the electronic [[Physics:Ground state|ground state]] and [[Physics:Excited state|excited states]] of individual atoms and molecules as well as the study of reaction pathways and [[Chemistry:Transition state|transition state]]s that occur during [[Chemistry:Chemical reaction|chemical reaction]]s. Spectroscopic properties may also be predicted. Typically, such studies assume the electronic wave function is adiabatically parameterized by the nuclear positions (i.e., the [[Physics:Born–Oppenheimer approximation|Born–Oppenheimer approximation]]). A wide variety of approaches are used, including semi-empirical methods, [[Density functional theory|density functional theory]], Hartree-Fock calculations, quantum [[Monte Carlo method|Monte Carlo]] methods, and [[Chemistry:Coupled cluster|coupled cluster]] methods.

Understanding [[Engineering:Electronic structure|electronic structure]] and [[Physics:Molecular dynamics|molecular dynamics]] through the development of computational solutions to the [[Physics:Schrödinger equation|Schrödinger equation]] is a central goal of quantum chemistry. Progress in the field depends on overcoming several challenges, including the need to increase the accuracy of the results for small molecular systems, and to also increase the size of large molecules that can be realistically subjected to computation, which is limited by scaling considerations — the computation time increases as a power of the number of atoms.

==History==
Some view the birth of quantum chemistry as starting with the discovery of the [[Physics:Schrödinger equation|Schrödinger equation]] and its application to the hydrogen atom. However, a 1927 article of [[Biography:Walter Heitler|Walter Heitler]] (1904–1981) and [[Biography:Fritz London|Fritz London]] is often recognized as the first milestone in the history of quantum chemistry.<ref>{{Cite journal |last=Heitler |first=W. |last2=London |first2=F. |date=1927 |title=Wechselwirkung neutraler Atome und homopolare Bindung nach der Quantenmechanik |url=http://dx.doi.org/10.1007/BF01397394 |journal=Zeitschrift für Physik |volume=44 |pages=455-472}}</ref> This was the first application of quantum mechanics to the diatomic hydrogen molecule, and thus to the phenomenon of the chemical bond.<ref>{{Cite book |last=Kołos |first=W. |url=https://doi.org/10.1007/978-94-009-0949-6_8 |title=Perspectives in Quantum Chemistry. Académie Internationale Des Sciences Moléculaires Quantiques/International Academy of Quantum Molecular Science |publisher=Springer |year=1989 |volume=6 |location=Dordrecht |chapter=The Origin, Development and Significance of the Heitler-London Approach}}</ref> However, prior to this a critical conceptual framework was provided by [[Biography:Gilbert N. Lewis|Gilbert N. Lewis]] in his 1916 paper ''The Atom and the Molecule'',<ref>{{Cite journal |last=Lewis |first=G.N. |title=The Atom and the Molecule |url=http://dx.doi.org/10.1021/ja02261a002 |journal=[[Organization:Journal of the American Chemical Society|Journal of the American Chemical Society]] |volume=38 |pages=762-785}}</ref> wherein Lewis developed the first working model of [[Physics:Valence electron|valence electrons]]. Important contributions were also made by Yoshikatsu Sugiura<ref>{{Cite journal |last=Sugiura |first=Y. |date=1927 |title=Über die Eigenschaften des Wasserstoffmoleküls im Grundzustande |url=https://link.springer.com/article/10.1007/BF01329207 |journal=Zeitschrift für Physik |volume=45 |pages=484-492}}</ref><ref>{{Cite journal |last=Nakane |first=Michiyo |date=2019 |title=Yoshikatsu Sugiura's Contribution to the Development of Quantum Physics in Japan |url=https://onlinelibrary.wiley.com/doi/10.1002/bewi.201900007 |journal=Berichte zur Wissenschaftsgeschichte |volume=42 |pages=338}}</ref> and S.C. Wang.<ref>{{Cite journal |last=Wang |first=S. C. |date=1928-04-01 |title=The Problem of the Normal Hydrogen Molecule in the New Quantum Mechanics |url=https://link.aps.org/doi/10.1103/PhysRev.31.579 |journal=Physical Review |volume=31 |issue=4 |pages=579–586 |doi=10.1103/PhysRev.31.579}}</ref> A series of articles by [[Biography:Linus Pauling|Linus Pauling]], written throughout the 1930s, integrated the work of Heitler, London, Sugiura, Wang, Lewis, and [[Biography:John C. Slater|John C. Slater]] on the concept of valence and its quantum-mechanical basis into a new theoretical framework.<ref>{{Cite journal |last=Pauling |first=Linus |date=April 6, 1931 |title=The nature of the chemical bond. Application of results obtained from the quantum mechanics and from a theory of paramagnetic susceptibility to the structure of molecules |url=http://scarc.library.oregonstate.edu/coll/pauling/bond/papers/1931p.3.html |journal=[[Organization:Journal of the American Chemical Society|Journal of the American Chemical Society]] |volume=53 |pages=1367-1400 |via=Oregon State University Library}}</ref> Many chemists were introduced to the field of quantum chemistry by Pauling's 1939 text ''The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry'', wherein he summarized this work (referred to widely now as [[Chemistry:Valence bond theory|valence bond theory]]) and explained quantum mechanics in a way which could be followed by chemists.<ref>{{Cite book |last=Pauling |first=Linus |title=The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry |publisher=Cornell University Press |year=1939 |edition=1st}}</ref> The text soon became a standard text at many universities. <ref>{{Cite web |last=Norman |first=Jeremy |title=Pauling Publishes "The Nature of the Chemical Bond" |url=https://historyofinformation.com/detail.php?id=3956 |access-date=July 11, 2023 |website=History of Information}}</ref> In 1937, [[Biography:Hans Hellmann|Hans Hellmann]] appears to have been the first to publish a book on quantum chemistry, in the Russian <ref>{{cite book|year=1937|last1=Хельман|first1=Г.|title=Квантовая Химия|publisher=Главная Редакция Технико-Теоретической Литературы, Moscow and Leningrad}}</ref> and German languages.<ref>{{cite book|year=1937|last1=Hellmann|first1=Hans|title=Einführung in die Quantenchemie|publisher= Deuticke, Leipzig und Wien}}</ref>

In the years to follow, this theoretical basis slowly began to be applied to chemical structure, reactivity, and bonding. In addition to the investigators mentioned above, important progress and critical contributions were made in the early years of this field by [[Biography:Irving Langmuir|Irving Langmuir]], [[Biography:Robert S. Mulliken|Robert S. Mulliken]], [[Biography:Max Born|Max Born]], [[Biography:J. Robert Oppenheimer|J. Robert Oppenheimer]], [[Biography:Hans Hellmann|Hans Hellmann]], [[Biography:Maria Goeppert Mayer|Maria Goeppert Mayer]], [[Biography:Erich Hückel|Erich Hückel]], [[Biography:Douglas Hartree|Douglas Hartree]], [[Biography:John Lennard-Jones|John Lennard-Jones]], and [[Biography:Vladimir Fock|Vladimir Fock]].

== Electronic structure ==

The '''electronic structure''' of an atom or molecule is the [[Physics:Quantum state|quantum state]] of its electrons.<ref>{{cite book|last=Simons|first=Jack|title=An introduction to theoretical chemistry|year=2003|publisher=Cambridge University Press|location=Cambridge, UK|chapter=Chapter 6. Electronic Structures|isbn=0521823609|url=http://simons.hec.utah.edu/ITCSecondEdition/chapter6.pdf}}</ref> The first step in solving a quantum chemical problem is usually solving the [[Physics:Schrödinger equation|Schrödinger equation]] (or [[Physics:Dirac equation|Dirac equation]] in [[Chemistry:Relativistic quantum chemistry|relativistic quantum chemistry]]) with the electronic molecular Hamiltonian, usually making use of the Born-Oppenheimer (B-O) approximation. This is called determining the electronic structure of the molecule.<ref>{{Cite book |last=Martin |first=Richard M. |title=Electronic Structure: Basic Theory and Practical Methods |date=2008-10-27 |publisher=Cambridge University Press |isbn=978-0-521-53440-6 |location=Cambridge |language=English}}</ref> An exact solution for the non-relativistic Schrödinger equation can only be obtained for the hydrogen atom (though exact solutions for the bound state energies of the [[Chemistry:Dihydrogen cation|hydrogen molecular ion]] within the B-O approximation have been identified in terms of the [[Lambert W function#Generalizations|generalized Lambert W function]]). Since all other atomic and molecular systems involve the motions of three or more "particles", their Schrödinger equations cannot be solved analytically and so approximate and/or computational solutions must be sought. The process of seeking computational solutions to these problems is part of the field known as [[Chemistry:Computational chemistry|computational chemistry]].

=== Valence bond theory ===
{{main|Chemistry:Valence bond theory}}

As mentioned above, Heitler and London's method was extended by Slater and Pauling to become the valence-bond (VB)
method. In this method, attention is primarily devoted to the pairwise interactions between atoms, and this method therefore correlates closely with classical chemists' drawings of [[Chemistry:Chemical bond|bonds]]. It focuses on how the atomic orbitals of an atom combine to give individual chemical bonds when a molecule is formed, incorporating the two key concepts of orbital hybridization and [[Chemistry:Resonance|resonance]].<ref>{{Cite book |last=Shaik |first=S.S. |title=A Chemist's Guide to Valence Bond Theory |last2=Hiberty |first2=P.C. |publisher=Wiley-Interscience |year=2007 |isbn=978-0470037355}}</ref>

=== Molecular orbital theory ===
[[File:Butadien4.jpg|thumb|300px|An anti-bonding molecular orbital of [[Chemistry:Butadiene|Butadiene]]]]
{{main|Chemistry:Molecular orbital theory}}

An alternative approach to valence bond theory was developed in 1929 by [[Biography:Friedrich Hund|Friedrich Hund]] and [[Biography:Robert S. Mulliken|Robert S. Mulliken]], in which [[Physics:Electron|electron]]s are described by mathematical functions delocalized over an entire [[Physics:Molecule|molecule]]. The Hund–Mulliken approach or molecular orbital (MO) method is less intuitive to chemists, but has turned out capable of predicting [[Physics:Spectroscopy|spectroscopic properties]] better than the VB method. This approach is the conceptual basis of the Hartree–Fock method and further post Hartree–Fock methods.

=== Density functional theory ===
{{main|Density functional theory}}

The [[Physics:Gas in a box|Thomas–Fermi model]] was developed independently by Thomas and [[Biography:Enrico Fermi|Fermi]] in 1927. This was the first attempt to describe many-electron systems on the basis of [[Physics:Electronic density|electronic density]] instead of [[Wave function|wave function]]s, although it was not very successful in the treatment of entire molecules. The method did provide the basis for what is now known as density functional theory (DFT). Modern day DFT uses the [[Physics:Kohn–Sham equations|Kohn–Sham method]], where the density functional is split into four terms; the Kohn–Sham kinetic energy, an external potential, exchange and correlation energies. A large part of the focus on developing DFT is on improving the exchange and correlation terms. Though this method is less developed than post Hartree–Fock methods, its significantly lower computational requirements (scaling typically no worse than ''n''<sup>3</sup> with respect to ''n'' basis functions, for the pure functionals) allow it to tackle larger polyatomic molecules and even [[Biology:Macromolecule|macromolecule]]s. This computational affordability and often comparable accuracy to [[Chemistry:Møller–Plesset perturbation theory|MP2]] and [[Chemistry:Coupled cluster|CCSD(T)]] (post-Hartree–Fock methods) has made it one of the most popular methods in [[Chemistry:Computational chemistry|computational chemistry]].

== Chemical dynamics ==
A further step can consist of solving the [[Physics:Schrödinger equation|Schrödinger equation]] with the total [[Physics:Molecular Hamiltonian|molecular Hamiltonian]] in order to study the motion of molecules. Direct solution of the Schrödinger equation is called ''[[Physics:Quantum dynamics|quantum dynamics]]'', whereas its solution within the [[Physics:Semiclassical physics|semiclassical]] approximation is called ''semiclassical dynamics.'' Purely [[Physics:Classical mechanics|classical]] simulations of molecular motion are referred to as ''[[Physics:Molecular dynamics|molecular dynamics]] (MD)''. Another approach to dynamics is a hybrid framework known as ''[[Chemistry:Mixed quantum-classical dynamics|mixed quantum-classical dynamics]];'' yet another hybrid framework uses the [[Physics:Path integral formulation|Feynman path integral]] formulation to add quantum corrections to molecular dynamics, which is called [[Path integral molecular dynamics|path integral molecular dynamics]]. Statistical approaches, using for example classical and quantum [[Monte Carlo method]]s, are also possible and are particularly useful for describing equilibrium distributions of states.

=== Adiabatic chemical dynamics ===
{{main|Physics:Born–Oppenheimer approximation}}
In adiabatic dynamics, interatomic interactions are represented by single [[Physics:Scalar|scalar]] [[Physics:Potential|potential]]s called [[Physics:Potential energy surface|potential energy surface]]s. This is the [[Physics:Born–Oppenheimer approximation|Born–Oppenheimer approximation]] introduced by [[Biography:Max Born|Born]] and Oppenheimer in 1927. Pioneering applications of this in chemistry were performed by Rice and Ramsperger in 1927 and Kassel in 1928, and generalized into the RRKM theory in 1952 by [[Biography:Rudolph A. Marcus|Marcus]] who took the [[Chemistry:Transition state|transition state]] theory developed by [[Biography:Henry Eyring (chemist)|Eyring]] in 1935 into account. These methods enable simple estimates of unimolecular reaction rates from a few characteristics of the potential surface.

=== Non-adiabatic chemical dynamics ===
{{main|Physics:Vibronic coupling}}

Non-adiabatic dynamics consists of taking the interaction between several coupled potential energy surface (corresponding to different electronic [[Physics:Quantum state|quantum state]]s of the molecule). The coupling terms are called vibronic couplings. The pioneering work in this field was done by Stueckelberg, Landau, and [[Biography:Clarence Zener|Zener]] in the 1930s, in their work on what is now known as the Landau–Zener transition. Their formula allows the transition probability between two [[Physics:Diabatic|diabatic]] potential curves in the neighborhood of an [[Physics:Avoided crossing|avoided crossing]] to be calculated. Spin-forbidden reactions are one type of non-adiabatic reactions where at least one change in [[Physics:Spin states (d electrons)|spin state]] occurs when progressing from [[Biology:Reagent|reactant]] to [[Chemistry:Product|product]].

== See also ==
{{colbegin}}
* [[Physics:Atomic physics|Atomic physics]]
* [[Chemistry:Computational chemistry|Computational chemistry]]
* [[Physics:Condensed matter physics|Condensed matter physics]]
* [[Physics:Car–Parrinello molecular dynamics|Car–Parrinello molecular dynamics]]
* [[Chemistry:Electron localization function|Electron localization function]]
* [[Organization:International Academy of Quantum Molecular Science|International Academy of Quantum Molecular Science]]
* [[Biology:Molecular modelling|Molecular modelling]]
* [[Chemistry:Physical chemistry|Physical chemistry]]
*[[Chemistry:Quantum computational chemistry|Quantum computational chemistry]]
* List of quantum chemistry and solid-state physics software
* [[Chemistry:QMC@Home|QMC@Home]]
* ''[[Biology:Quantum Aspects of Life|Quantum Aspects of Life]]''
* [[Chemistry:Quantum electrochemistry|Quantum electrochemistry]]
* [[Chemistry:Relativistic quantum chemistry|Relativistic quantum chemistry]]
* [[Physics:Theoretical physics|Theoretical physics]]
*Spin forbidden reactions{{colend}}

==References==
{{reflist}}

==Sources==
* {{cite book |last1=Atkins|first1= P.W.|publisher=Oxford University Press|isbn= 0-19-879285-9| title=Physical Chemistry|year= 2002}}
* {{cite book |last1=Atkins|first1= P.W.|last2= Friedman|first2= R. |year=2005| title=Molecular Quantum Mechanics|publisher=Oxford University Press|edition= 4th |isbn= 978-0-19-927498-7}}
* {{cite book |last1=Atkins|first1= P.W.| last2= Friedman|first2= R. |year=2008|title=Quanta, Matter and Change: A Molecular Approach to Physical Change| isbn= 978-0-7167-6117-4}}
* {{cite book |last=Bader|first=Richard|title=Atoms in Molecules: A Quantum Theory|publisher=Oxford University Press|year=1994|isbn=978-0-19-855865-1|}}
* Gavroglu, Kostas; Ana Simões: ''Neither Physics nor Chemistry: A History of Quantum Chemistry'', MIT Press, 2011, {{ISBN|0-262-01618-4}}
* Karplus M., Porter R.N. (1971). ''Atoms and Molecules. An introduction for students of physical chemistry'', Benjamin–Cummings Publishing Company, {{ISBN|978-0-8053-5218-4}}
* {{cite book |last1=Landau | first1= L.D. |last2= Lifshitz|first2=E.M. |title=Quantum Mechanics:Non-relativistic Theory| series=Course of Theoretical Physic| year= 1977 |volume= 3 |publisher=Pergamon Press| isbn=0-08-019012-X}}
* {{cite book |last=Levine|first= I. |year=2008|title=Physical Chemistry|publisher=McGraw–Hill Science|edition= 6th| isbn =978-0-07-253862-5}}
* {{cite book| last=McWeeny| first= R. |title=Coulson's Valence| year= 1979 |publisher=Oxford Science Publications|isbn= 0-19-855144-4}}
* {{cite book| author=Pauling, L.| title=General Chemistry|publisher=Dover Publications|year=1954|isbn=0-486-65622-5|url-access=registration|url=https://archive.org/details/generalchemistry00paul_0}}
* {{cite book| author1-last=Pauling|author1-first= L.| author2-last=Wilson|author2-first= E. B. |orig-year=1935|year=1963|title=Introduction to Quantum Mechanics with Applications to Chemistry| publisher=Dover Publications| isbn =0-486-64871-0}}
* {{cite book |last1=Pullman |first1=Bernard |first2= Alberte |last2=Pullman|year=1963|title=Quantum Biochemistry|location=New York and London| publisher=Academic Press| isbn=90-277-1830-X}}
* {{cite book |last= Scerri|first= Eric R.|title= The Periodic Table: Its Story and Its Significance|publisher= Oxford University Press|year= 2006|isbn= 0-19-530573-6|url-access= registration|url= https://archive.org/details/periodictableits0000scer}} Considers the extent to which chemistry and especially the periodic system has been reduced to quantum mechanics.
* {{cite book| last= Simon |first=Z. | year=1976| title=Quantum Biochemistry and Specific Interactions| publisher=Taylor & Francis| isbn =978-0-85626-087-2 }}
* {{cite book |last1=Szabo| first1=Attila|first2=Neil S.|last2= Ostlund|year=1996|title=Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory|publisher= Dover| isbn= 0-486-69186-1}}

== External links ==
* [http://vergil.chemistry.gatech.edu/notes/index.html The Sherrill Group – Notes]
* [http://www.shodor.org/chemviz/ ChemViz Curriculum Support Resources]
* [http://www.quantum-chemistry-history.com/ Early ideas in the history of quantum chemistry]

{{BranchesofChemistry|state=expanded}}
{{Quantum mechanics topics}}

{{DEFAULTSORT:Quantum Chemistry}}
[[Category:Quantum chemistry| ]]

{{Sourceattribution|Quantum chemistry}}

Physics:Quantum chemistry - Revision history

imported>WikiHarold: WikiHarold moved page Chemistry:Quantum chemistry to Physics:Quantum chemistry without leaving a redirect

imported>WikiHarold: WikiHarold moved page Chemistry:Quantum chemistry to Physics:Quantum chemistry without leaving a redirect