Can the Band Structure Diagram be Represented in Real Space Instead of k-Space?

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Discussion Overview

The discussion centers on the possibility of representing band structure diagrams in real space instead of the conventional k-space. Participants explore the implications and usefulness of such a representation, considering both theoretical and practical aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether band structure diagrams can be depicted in real space, suggesting it may be legal but not commonly done due to a perceived lack of instructiveness.
  • One participant argues that a 3D Fourier transform could yield a real space representation, but notes it would not be called a "band diagram" since it would not plot energy versus k.
  • Another participant believes that a real space representation could be useful, as it might illustrate how energy varies with distance from ions and highlight the periodic nature of the potential.
  • Concerns are raised about the absence of certain features, like the band gap, in a real space representation, questioning its overall utility.
  • A participant suggests that a 1-D Fourier transform could also be performed, transitioning from k-space to real space.
  • One contributor proposes that analyzing a single dispersion curve at a given eigenvalue through Fourier transformation could provide insights into the energy of an electron versus distance in the lattice, while also discussing the implications of periodicity on k-values.
  • Another participant recommends a practical approach of plotting kinetic and potential energy components as a function of distance to gain insights, although they imply that the conventional E vs. X relation is more commonly used for clarity.

Areas of Agreement / Disagreement

Participants express differing views on the usefulness and feasibility of representing band structure in real space. There is no consensus on whether such a representation would provide valuable insights or if it is inherently less instructive than the traditional k-space diagrams.

Contextual Notes

Participants note limitations regarding the potential loss of information, such as the band gap, in a real space representation. The discussion also reflects on the periodicity of the lattice and its implications for electron behavior, which may complicate the interpretation of results.

BeauGeste
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So band structure diagrams are always depicted in k-space (1st BZ -pi/a to pi/a).
Is it possible to show them in real space (1st WS cell -a/2 to a/2)?
It seems to me that this would be legal. Is it not done because it is not instructive?
 
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If you can do a 3D Fourier transform, you can get that. However, you can't call it "band dragram", because it won't be E vs. k anymore.

We don't do it because it tells us nothing useful.

Zz.
 
I think it would be useful. It would show how the energy varies with distance from ions. It would show the periodic nature of the potential in real space (slightly less abstract). Is it less useful because an idea like band gap would not show up?
Also there's no reason you can't do it in 1-D too, right? Just a 1-D Fourier transform going from kx->x.
 
BeauGeste,

My intuition tells me that if you took a single dispersion curve (the E vs k curves) at a given eigenvalue (say n = 1) and did a Fourier transform on the function you would get a function describing the total energy of a electron vs distance in the lattice for a given k. However, for a given n and k the energy of a electron is fixed. What I think you want to determine is the potential, kinetic energy components as a function of distance in the the lattice.

Remember due to periodicity, electrons on the same dispersion curve have k-values dependent on the dimensions of the lattice and the k-values of two electrons with the same spin cannot be the same.

Anyways, to satisfy yourself I would suggest taking a eigenfunction of the Kronig-Penney Hamiltonian at a value of k and determine the eigenvalue of that eigenfunction. Plot it as a function of distance. Then plot the kinetic/potential energy components as a function of distance. It will give information that you already should intuitively know. Thats why we don't use the E vs. X relation.

Best Regards
Modey3
 
Last edited:

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