Bloch's theorem infinite system?

Click For Summary
SUMMARY

In infinite systems, Bloch's theorem necessitates that the wave vector k be real to maintain the physicality of the wavefunction. The divergence of the wavefunction in infinite systems leads to unphysical results unless k is constrained to real values. The reduced Hamiltonian, defined as H=p²/2m + V, is only self-adjoint under periodic boundary conditions, which require that u(a) = u(0)exp(ika). This relationship is crucial for ensuring the validity of the wavefunction in an infinite context.

PREREQUISITES
  • Understanding of Bloch's theorem
  • Familiarity with quantum mechanics concepts, particularly wavefunctions
  • Knowledge of Hamiltonians in quantum systems
  • Experience with periodic boundary conditions in physics
NEXT STEPS
  • Study the implications of periodic boundary conditions in quantum mechanics
  • Explore the derivation and applications of Bloch's theorem
  • Investigate self-adjoint operators in quantum mechanics
  • Read the article on self-adjoint extensions and their significance in quantum systems
USEFUL FOR

Physicists, quantum mechanics students, and researchers interested in the mathematical foundations of wavefunctions and their applications in infinite systems.

thegirl
Messages
40
Reaction score
1
Hi,

Does anyone know why k has to be real in an infinite system for bloch's theorem. I understand that the wavefunction becomes unphysical in an infinite system as it diverges. Why does that mean k has to be real?

f(x)=u(x)exp(ikx)
 
Physics news on Phys.org
Infinite systems are always quite difficult to discuss. A sound way to discuss this problem is to look at the reduced hamiltonian ##H=p^2/2m +V## acting on the functions u(x) defined on the range [0, a] where a is the length of the elementary cell. It turns out that this hamiltonian is only self-adjoint for periodic boundary conditions so that ##u(a)=u(0)\exp(ika)## where k labels all possible self-adjoint extensions. This is discussed in a pedagogical way in this article:
http://scitation.aip.org/content/aapt/journal/ajp/69/3/10.1119/1.1328351
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 20 ·
Replies
20
Views
7K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
8K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 11 ·
Replies
11
Views
7K
  • · Replies 9 ·
Replies
9
Views
3K