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| In [[quantum chemistry]], '''size consistency''' and '''size extensivity''' are concepts about how the behaviour of a quantum chemistry calculations changes with size. '''Size consistency''' (or '''strict separability''') is a property that guarantees the [[consistency]] of the energy behaviour when interaction between the involved molecular system is nullified (for example, by distance). '''Size-extensivity''', introduced by Bartlett, is a more mathematically formal characteristic which refers to the correct (linear) scaling of a method with the number of electrons.<ref>{{cite journal|doi=10.1146/annurev.pc.32.100181.002043|first=R. J.|last= Bartlett|title=Many-Body Perturbation Theory and Coupled Cluster Theory for Electron Correlation in Molecules|journal= Annual Review of Physical Chemistry|volume=32|page=359 |year=1981}}</ref>
| | The writer is known as Wilber Pegues. To play lacross is something I truly appreciate performing. I am an invoicing officer and I'll be promoted soon. For years he's been residing in Alaska and he doesn't plan on altering it.<br><br>my web page: online psychic reading; [http://kard.dk/?p=24252 Continuing], |
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| Let A and B be two non-interacting systems. If a given theory for the evaluation of the energy is size consistent, then the energy of the supersystem A-B is equal to the sum of the energy of A plus the energy of B taken by themselves (<math>E(A-B) = E(A) + E(B)</math>). This property of size consistency is of particular importance to obtain correctly behaving dissociation curves. Others have more recently argued that the entire potential energy surface should be well-defined.<ref>{{cite book| first=P. R. |last=Taylor|title= Lecture Notes in Quantum Chemistry: European Summer School|publisher=Springer-Verlag|location= Berlin|year= 1994|pages=125–202}}</ref>
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| Size consistency and size extensivity are sometimes used interchangeably in the literature, However there are very important distinctions to be made between them. <ref>{{cite web|url=http://www.uam.es/docencia/quimcursos/Docs/Knowledge/Fundamental_Theory/cc/node7.html |title=Size-Extensivity and Size-Consistency |publisher=Uam.es |date=1995-01-20 |accessdate=2014-02-01}}</ref> [[Hartree-Fock]], [[coupled cluster]], many-body [[perturbation theory (quantum mechanics)|perturbation theory]] (to any order), and full [[configuration interaction]] (CI) are size extensive but not always size consistent. For example the Restricted [[Hartree-Fock]] model is not able to described correctly the dissociation curves of H2 and therefore all post HF methods will fail in that matter (except FCI). Sometimes numerical errors can cause a method that is formally size-consistent to behave in a non-size-consistent manner.<ref>{{Cite journal|last1=Van Dam|first1=Huub|last2=Van Lenthe|first2=Joop|last3=Pulay|first3=Peter|title=The size consistency of multi-reference Møller-Plesset perturbation theory|journal=Molecular Physics|volume=93|page=431|year=1998|doi=10.1080/002689798169122|issue=3 }}</ref>
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| '''Core-extensivity''' is yet another related property, which extends the requirement to the proper treatment of excited states.<ref>{{cite journal|last1=Mukhopadhyay|first1=S|title=A comparative study of core-extensive and core—valence-extensive coupled-cluster theories for energy differences: Excitation energies|journal=Chemical Physics Letters|volume=173|page=181|year=1990|doi=10.1016/0009-2614(90)80074-N|last2=Chaudhuri|first2=Rajat|last3=Mukhopadhyay|first3=Debasis|last4=Mukherjee|first4=Debashis|issue=2–3}}</ref>
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| ==References==
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| {{Reflist}}
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| [[Category:Quantum chemistry]]
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| {{chem-stub}}
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Latest revision as of 16:55, 3 November 2014
The writer is known as Wilber Pegues. To play lacross is something I truly appreciate performing. I am an invoicing officer and I'll be promoted soon. For years he's been residing in Alaska and he doesn't plan on altering it.
my web page: online psychic reading; Continuing,