K vector in first brillouin zone

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Discussion Overview

The discussion centers on the concept of K vectors in the context of the first Brillouin Zone and their relationship to reciprocal space and reciprocal lattices. Participants explore the definitions and implications of these concepts, particularly in relation to wavefunctions and electron density in crystals.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about how K vectors can be said to "live" in the first Brillouin Zone if they cannot be represented in the vector form of reciprocal space.
  • Another participant clarifies the distinction between reciprocal space and reciprocal lattice, noting that any point in reciprocal space can be decomposed into a point within the first Brillouin Zone and a reciprocal lattice vector.
  • A further contribution suggests that there are K vectors associated with the reciprocal lattice, which have the same periodicity as the real lattice, and distinguishes these from other wavevectors that can propagate through the medium.
  • One participant proposes that an example illustrating the splitting of a general wavevector into a vector in the first Brillouin Zone and a reciprocal lattice vector could be beneficial.
  • A later reply indicates that the initial confusion has been resolved, suggesting a better understanding of the topic.

Areas of Agreement / Disagreement

Participants appear to be exploring the topic with some agreement on the definitions of K vectors and their relation to reciprocal space, but the initial confusion indicates that there may still be nuances that are not fully resolved.

Contextual Notes

There are potential limitations in understanding related to the definitions of reciprocal space and reciprocal lattice, as well as the implications of wavevector decomposition that remain to be fully clarified.

Who May Find This Useful

This discussion may be useful for students and researchers interested in solid-state physics, particularly those studying crystallography, band theory, and wave propagation in periodic structures.

Sophocles
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Hey guys,

I just realized that there is a gap somewhere in my understanding of K vectors and reciprocal space.
My question is how can we talk about K vectors "living" in the first Brillouin Zone, when these vectors cannot be expressed on the vector form of reciprocal space ( r*=ha*kb*+lc* , where h,k,l integers)? First Brillouin Zone as I understand it, extends until half the length of the first neighboring lattice point of the reciprocal space.
 
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If I interprete your question correctly, you seem to be confusing the reciprocal space and reciprocal lattice.
For example the electron density or wavefunction of some crystal is defined for any point in space and likewise is its Fourier transform defined for any k vector with real components in reciprocal space.
In direct space any location in the crystal can be described as a lattice vector plus some vector lying in the unit cell centered at the origin.
Likewise, any point in reciprocal space can be decomposed into a point inside the first brillouin zone and a reciprocal lattice vector.
 
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Ok. So if I get it correctly, there are k vectors who belong to the reciprocal lattice, having periodicity the same as the real lattice (and the ones responsible for diffraction phenomena) and then there is K space for all the rest of the waves that can travel through the medium?
 
Maybe it is helpful to have some example, where splitting a general wavevector into a vector k in the first BZ and a reciprocal lattice vector is useful:
http://en.wikipedia.org/wiki/Bloch_wave
 
Thank you very much DrDu. After all, I finally got it!
 

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