Theoretical chemistry
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'''Theoretical chemistry''' involves the use of physics to explain or predict [[chemistry|chemical]] phenomena. In recent years, it has consisted primarily of [[quantum chemistry]], i.e., the application of [[quantum mechanics]] to problems in chemistry. Theoretical chemistry may be broadly divided into electronic structure, dynamics, and statistical mechanics. In the process of solving the problem of predicting chemical [[reactivity|reactivities]], these may all be invoked to various degrees. Other "miscellaneous" research areas in theoretical chemistry include the mathematical characterization of bulk chemistry in various phases (e.g. the study of [[chemical kinetics]]) and the study of the applicability of more recent math developments to the basic areas of study (e.g. for instance the possible application of principles of topology to the study of electronic structure.) The latter area of theoretical chemistry is sometimes referred to as [[mathematical chemistry]].
Much of this may be categorized as [[computational chemistry]], although computational chemistry usually refers to the application of theoretical chemistry in an applied setting, usually with some approximation scheme such as certain types of [[post Hartree-Fock]], [[Density Functional Theory]], [[Computational chemistry#Semiempirical methods|semiempirical methods]] (like for instance [[PM3 (chemistry)|PM3]]) or [[Force field (chemistry)|force field]] methods. Some chemical theorists apply [[statistical mechanics]] to provide a bridge between the microscopic phenomena of the quantum world and the macroscopic bulk properties of systems.
Theoretical attacks on chemical problems go back to the earliest days, but until the formulation of the [[Schrödinger equation]] by the [[Austria]]n [[physics|physicist]] [[Erwin Schrödinger]], the techniques available were rather crude and speculative. Currently, much more sophisticated theoretical approaches, based on [[Quantum Field Theory]] and Nonequilibrium Green Function Theory are in vogue.
== Branches of theoretical chemistry ==
;[[Quantum chemistry]]: The application of [[quantum mechanics]] to chemistry
;[[Computational chemistry]]: The application of [[computer code]]s to chemistry
;[[Molecular modelling]]: Methods for modelling molecular structures without necessarily referring to quantum mechanics. Examples are [[docking (molecular)|molecular docking]], [[protein-protein docking]], [[drug design]], [[combinatorial chemistry]].
;[[Molecular dynamics]]: Application of [[classical mechanics]] for simulating the movement of the nuclei of an assembly of atoms and molecules.
;[[Molecular mechanics]]: Modelling of the intra- and inter-molecular interaction [[potential energy surface]]s via a sum of interaction [[force]]s.
;[[Mathematical chemistry]]: Discussion and prediction of the molecular structure using mathematical methods without necessarily referring to quantum mechanics.
;Theoretical [[chemical kinetics]]: Theoretical study of the [[dynamical system]]s associated to reactive [[chemical]]s and their corresponding [[differential equation]]s.
== Closely related disciplines ==
Historically, the major field of application of theoretical chemistry has been in the following fields of research:
*[[Atomic physics]]: The discipline dealing with electrons and atomic nuclei.
*[[Molecular physics]]: The discipline of the electrons surrounding the molecular nuclei and of movement of the nuclei. This term usually refers to the study of molecules made of a few atoms in the gas phase. But some consider that molecular physics is also the study of bulk properties of chemicals in terms of molecules.
*[[Physical chemistry]] and [[chemical physics]]: Chemistry investigated via physical methods like [[laser]] techniques, [[scanning tunneling microscope]], etc. The formal distinction between both fields is that physical chemistry is a branch of chemistry while chemical physics is a branch of physics. In practice this distinction is quite vague.
*[[Many-body theory]]: The discipline studying the effects which appear in systems with large number of constituents. It is based on [[quantum physics]] - mostly [[second quantization]] formalism - and [[quantum electrodynamics]].
Hence, the theoretical chemistry discipline is sometimes seen as a branch of those fields of research. Nevertheless, more recently, with the rise of the [[density functional theory]] and other methods like [[molecular mechanics]], the range of application has been extended to chemical systems which are relevant to other fields of chemistry and physics like [[biochemistry]], [[condensed matter physics]], [[nanotechnology]] or [[molecular biology]].
== Bibliography ==
* Attila Szabo and Neil S. Ostlund, ''Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory'', Dover Publications; New Ed edition (1996) ISBN-10: 0486691861, ISBN-13: 978-0486691862
== Quotations ==
{{Cquote2|quotetext=The deepest part of Theoretical Chemistry must end up in Quantum Mechanics.|personquoted=R. P. Feynman|quotesource=''The Feynman Lectures on Physics''|quotewidth=15px|quoteheight=15px}}
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[[Category:Theoretical chemistry| ]]
[[Category:Chemistry]]
[[bn:তাত্ত্বিক রসায়ন]]
[[ca:Química teòrica]]
[[cs:Teoretická chemie]]
[[de:Theoretische Chemie]]
[[es:Química teórica]]
[[eo:Teoria kemio]]
[[fr:Chimie théorique]]
[[id:Kimia teori]]
[[he:כימיה תאורטית]]
[[lmo:Chímica teorica]]
[[nl:Theoretische chemie]]
[[ja:理論化学]]
[[no:Teoretisk kjemi]]
[[pl:Chemia teoretyczna]]
[[sv:Teoretisk kemi]]
[[zh:理论化学]]