Validity of virial theorem in QM

In summary, the conversation discusses the standard derivation of the virial theorem and how it assumes working in the energy basis. One key relation in this derivation is <T> = n/(n+2) <H>, which does not hold for the continuous spectrum of Coulomb potential where both <T> and <H> are positive and n/(n+2) = -1. The conversation also explores where in the derivation the assumption of dealing with bound states is used, with one participant mentioning that it is based on the evaluation of the term <[H, pr]>. In the case of bound states, this term results in a finite value due to (E-E)=0, while in the case of continuum states, it diver
  • #1
Heirot
151
0
In the standard derivation of the virial theorem, one assumes to be working in the energy basis. One then gets <T> = n/(n+2) <H>. This relation doesn't hold for the continuous spectrum of Coulomb potential where <T> > 0, <H> > 0, n/(n+2) = -1. So, where in the derivation did we use the fact we were dealing with bound states?
 
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  • #2
If I remember correctly, the relation is based on evaluation of the term
[tex] \langle [H,\mathbf{pr}]\rangle=(E-E) \langle \mathbf{pr}\rangle [/tex].
In the case of bound states, (E-E)=0 and [tex] \langle \mathbf{pr}\rangle [/tex] is finite. In the case of continuum states, the last average diverges, so that one cannot conclude that the whole expression vanishes.
 
  • #3
Oh, I see - Thank you!
 

Related to Validity of virial theorem in QM

1. What is the virial theorem in quantum mechanics?

The virial theorem in quantum mechanics is a mathematical expression that relates the average kinetic energy of a system to the average potential energy. It is used to describe the behavior of particles in a quantum system, such as atoms or molecules.

2. Is the virial theorem valid in quantum mechanics?

Yes, the virial theorem is valid in quantum mechanics. It has been proven to hold for systems described by the Schrödinger equation, which is the fundamental equation of quantum mechanics.

3. How does the virial theorem relate to the uncertainty principle?

The virial theorem is closely related to the uncertainty principle in quantum mechanics. The uncertainty principle states that it is impossible to simultaneously know the exact position and momentum of a particle. The virial theorem shows that in a quantum system, the average kinetic energy and potential energy are related to the uncertainty in position and momentum, respectively.

4. Can the virial theorem be applied to all quantum systems?

The virial theorem can be applied to most quantum systems, including atoms, molecules, and subatomic particles. However, it may not hold for systems that are subject to strong external forces or are in highly excited states.

5. How is the virial theorem used in practical applications?

The virial theorem is used in many practical applications, such as in spectroscopy to determine the energy levels of atoms and molecules. It is also used in molecular dynamics simulations to study the behavior of molecules and in quantum chemistry calculations to predict the properties of chemical compounds.

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