Extended hamiltonian operator for the Hydrogen atom

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Discussion Overview

The discussion revolves around the possibility of extending the Hamiltonian of the hydrogen atom to include half-integer spin, particularly in the context of relativistic quantum mechanics. Participants explore theoretical frameworks and references related to this topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses familiarity with the standard hydrogen atom solution and questions the extension of the Hamiltonian to include half-integer spin, suggesting that spin may only arise in relativistic contexts.
  • Another participant agrees that in a non-relativistic framework, electron spin does not naturally enter the Hamiltonian, noting that it can be included as a perturbation.
  • A different participant asserts that it is indeed possible to extend the Hamiltonian using the Levy-Leblond approach, countering the initial guess about the necessity of relativistic treatment for spin.
  • References to specific texts are provided, including "Modern Quantum Mechanics" by Sakurai and Napolitano, and "Quantum Mechanics. An Introduction" by Walter Greiner, which discuss relevant theories and equations.
  • Participants mention the Pauli equation as a non-relativistic limit of the Dirac equation and refer to group-theoretical approaches to wave equations by physicists Fushchich and Nikitin.

Areas of Agreement / Disagreement

Participants express differing views on the role of relativistic quantum mechanics in incorporating spin into the Hamiltonian, with some asserting that it can be done through specific theoretical frameworks while others maintain that spin is inherently a relativistic phenomenon. The discussion remains unresolved regarding the best approach to extend the Hamiltonian.

Contextual Notes

There are references to specific texts and theories, but the discussion does not resolve the assumptions or limitations of the proposed approaches, nor does it clarify the mathematical steps involved in the extension of the Hamiltonian.

PedroBittar
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I am familiar with the usual solution of the hydrogen atom using the associated legendre functions and spherical harmonics, but my question is: is it possible to extend the hamiltonian of the hydrogen atom to naturally encompass half integer spin?
My guess is that spin only pops in naturally in relativistic quantum mechanics, but since my knowledge on the subject is limited I am not sure how to proceed with the argument and would appreciate some references with more complete discussions.
 
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PedroBittar said:
My guess is that spin only pops in naturally in relativistic quantum mechanics
Your guess hits the point. If you stay non-relativistic, electron spin never enters the Hamiltonian of a Hydrogen-like atom (there is a perturbation method to account for the effect of spin, but as you might know a perturbation is something you add into the original model, it's not something you start off from the beginning). In fact, the relativistic effect in atom is best described through Dirac equation. For a more detailed discussion you may try chapter 8 in "Modern Quantum Mechanics" 2nd edition by Sakurai and Napolitano.
 
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PedroBittar said:
I am familiar with the usual solution of the hydrogen atom using the associated legendre functions and spherical harmonics, but my question is: is it possible to extend the hamiltonian of the hydrogen atom to naturally encompass half integer spin? [...]

Yes, it is possible to extend the Hamiltonian by the Levy-Leblond approach.

PedroBittar said:
[...] My guess is that spin only pops in naturally in relativistic quantum mechanics, but since my knowledge on the subject is limited I am not sure how to proceed with the argument and would appreciate some references with more complete discussions.

Your guess is wrong. Levy-Leblond's work is the subject of chapter 13 of Walter Greiner's "Quantum Mechanics. An Introduction", Springer Verlag.
Actually, Pauli's equation is the simplest Galilei-group invariant wave equation, just in the same vein as the Dirac one is the simplest Poincaré-group invariant group equation. There were/are two famous Ukrainian physicists, Fushchich and Nikitin who wrote a whole book on group-theoretical derivations of wave equations

upload_2017-3-19_23-43-37.png
 
dextercioby said:
Yes, it is possible to extend the Hamiltonian by the Levy-Leblond approach.
Your guess is wrong. Levy-Leblond's work is the subject of chapter 13 of Walter Greiner's "Quantum Mechanics. An Introduction", Springer Verlag.
Actually, Pauli's equation is the simplest Galilei-group invariant wave equation, just in the same vein as the Dirac one is the simplest Poincaré-group invariant group equation. There were/are two famous Ukrainian physicists, Fushchich and Nikitin who wrote a whole book on group-theoretical derivations of wave equations

View attachment 114767
That is very interesting, and makes a lot of sense since the pauli equation seems to be the nonrelativistic limit of dirac equation.
Thanks, I will definitely take a look on this group theory derivations.
 

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