3-D harmonic oscillator expectation value

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SUMMARY

The forum discussion centers on the calculation of the expectation value for a 3-D harmonic oscillator using the trial wavefunction ##ψ=e^{-αr}##. The Hamiltonian is applied to this wavefunction, leading to the expression ##<ψ|H|ψ>/<ψ|ψ> = (\hbarα)^2/2m + 3mω^2/2α^2##. A critical point raised involves the integration measure, specifically the inclusion of the term ##r^2 dr## in the volume element, which is essential for correctly evaluating the integral. The discussion highlights the importance of recognizing the limits of the provided integral for negative powers.

PREREQUISITES
  • Understanding of quantum mechanics, specifically the concept of Hamiltonians.
  • Familiarity with spherical polar coordinates in quantum systems.
  • Knowledge of trial wavefunctions and their application in variational methods.
  • Proficiency in performing integrals involving exponential functions and their limits.
NEXT STEPS
  • Review the derivation of the Hamiltonian for the 3-D harmonic oscillator in spherical coordinates.
  • Study the application of trial wavefunctions in quantum mechanics, focusing on variational principles.
  • Learn about the significance of integration measures in quantum mechanical calculations.
  • Explore advanced integration techniques for handling exponential functions with varying limits.
USEFUL FOR

Students and researchers in quantum mechanics, particularly those working on harmonic oscillators and variational methods, will benefit from this discussion.

dyn
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Homework Statement


The Hamiltonian for the 3-D harmonic oscillator in spherical polar coordinates is given in the question.The question then asks : using the trial wavefunction ##ψ=e^(-αr) ## show that


Homework Equations



##<ψ|H|ψ>/<ψ|ψ> = (\hbarα)^2/2m + 3mω^2/2α^2##

The following integral is also given## ∫ x^nexp(-ax) = n!/a^(n+1) ##for n≥0 with limits from 0 to ∞

The Attempt at a Solution



I applied the Hamiltonian to ψ. The \theta and \phi terms drop out. I then perform the integral of ∫ ψ^*Hψ but I have a term containing 1/r and the given integral doesn't apply for n<0
 
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Please show your work.
 
dyn said:

Homework Statement


The Hamiltonian for the 3-D harmonic oscillator in spherical polar coordinates is given in the question.The question then asks : using the trial wavefunction ##ψ=e^(-αr) ## show that


Homework Equations



##<ψ|H|ψ>/<ψ|ψ> = (\hbarα)^2/2m + 3mω^2/2α^2##

The following integral is also given## ∫ x^nexp(-ax) = n!/a^(n+1) ##for n≥0 with limits from 0 to ∞

The Attempt at a Solution



I applied the Hamiltonian to ψ. The \theta and \phi terms drop out. I then perform the integral of ∫ ψ^*Hψ but I have a term containing 1/r and the given integral doesn't apply for n<0
What did you use for the measure of integration dV? It contains ## r^2 dr##, did you forget that ##r^2##?
 

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