Kronig-Penney model only with cosh

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Discussion Overview

The discussion revolves around the application of the Kronig-Penney model in quantum mechanics, specifically focusing on the choice of eigenfunctions in regions of high potential energy for bound states. Participants explore the implications of using different forms of the eigenfunctions and the symmetry considerations involved.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Felix questions why the eigenfunctions in high potential energy regions cannot be expressed as Acosh(Qx+m) instead of the more general form A'cosh(Qx)+B'sinh(Qx), suggesting that symmetry considerations should allow for the simplification.
  • One participant asserts that the simplification is valid only for the lowest energy state (k=0), indicating that for states with different wavevectors, the symmetry is disrupted by the exp(ikx) term.
  • Felix expresses confusion regarding the symmetry breaking, questioning whether the requirement for mirror symmetry applies only to the probability density and not the wavefunction itself, noting that sinh^2 is mirror symmetric around the origin.
  • Another participant requests clarification on the specific Hamiltonian and wavefunctions being discussed, indicating a need for more precise definitions in the conversation.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the symmetry of wavefunctions and the implications of different eigenfunction forms. No consensus has been reached on the appropriateness of using Acosh(Qx+m) in the context described.

Contextual Notes

Participants have not fully specified the Hamiltonian or the exact wavefunctions in question, which may limit the clarity of the discussion. Additionally, the assumptions regarding symmetry and the conditions under which different eigenfunction forms apply remain unresolved.

8Apeiron8
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Hey!

Why i can't use as approach for the eigenfunctions in the regions of high potential energy for bound states only Acosh(Qx+m) instead of A'cosh(Qx)+B'sinh(Qx), where m is the midpoint of the wall?

If i put the origin of the coordinate system in this midpoint and use the mirror-symmetry of the chrystal, the sinh term must vanish.

Many thanks,

Felix
 
Last edited:
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You can do so for the state of lowest energy or k=0. For states with different wavevector k, the symmetry is broken by the exp(ikx) term.
 
Sry but i don't understand this. The exp(ikx) term is part of the approach for the region with low potential energy, why it breaks the symmetry in the other region?

Could the reason be, that only the probability density must be mirror symmetric but not the wavefunction?

sinh^2 is mirror symmetric around the origin!
 
Last edited:
Maybe you could specify exactly the hamiltonian and the wavefunctions you are talking about?
 

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