Talk:Perturbation theory
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[edit] Linear combination of atomic orbitals molecular orbital method
I have edited the history section as the LCAO method was introduced by Sir John Lennard-Jones in 1929, not by Fano. However, in what way is this method perturbation theory? What is the unperturbed function? What is the perturbation? I would call it a variational method in contrast to perturbational methods in quantum chemistry. --Bduke 08:06, 10 June 2007 (UTC)
- This is explained a bit here. However, variational methods can be used to derive non-perturbative results (i.e. effects that vanish to all orders in perturbation theory). So, in general, variational methods are not equivalent to perturbation theory. Count Iblis 14:23, 10 June 2007 (UTC)
- Indeed but LCAO itself is not perturbation theory. It is used in Hartree-Fock theory get the unperturbed reference in methods like MP2. It is the section on LCAO that I think should be removed from this article. LCAO is a variational method, which as you say is not equivalent to perturbation theory. --Bduke 01:12, 11 June 2007 (UTC)
- Yes, I agree with removal of that section. I'm not sure if other editors want to give their opinion, so let's wait a few days... Count Iblis 13:05, 12 June 2007 (UTC)
- Indeed but LCAO itself is not perturbation theory. It is used in Hartree-Fock theory get the unperturbed reference in methods like MP2. It is the section on LCAO that I think should be removed from this article. LCAO is a variational method, which as you say is not equivalent to perturbation theory. --Bduke 01:12, 11 June 2007 (UTC)
[edit] epicycles
The sentence about 17th century epicycles in the history of PT sounds strange to me. In the first place epicycles became less important after Keppler's work of around 1610. In the second place, if epicycles have anything to do with PT, then the origin of PT goes back to Ptolemy (150) and Hipparchos (100 BC). Any expert opinions? In any case a source is indispensable.--P.wormer 09:28, 12 June 2007 (UTC)
[edit] History
Perturbation theory has its roots in 17th century celestial mechanics, where the theory of epicycles was used to make small corrections to the predicted paths of planets.[citation needed] Curiously, it was the need for more and more epicycles that eventually led to the 16th century Copernican revolution in the understanding of planetary orbits. [The previous sentence is mistaken: it is a common misunderstanding that Copernicus did away with epicycles. However, a close examination of Copernicus' great treatise, the De Revolutionibus reveals that, not only does Copernicus freely employ epicycles, but that he commits many of the same offenses in his planetary models as both he and the Tradition had accused Ptolemy of doing.]PtolemyGalen 17:36, 28 August 2007 (UTC)
