quantum multipole expansion

You’ll need to know what perturbation theory is before you can tackle this video. If perturbation theory is not familiar to you (any more), you can brush up your knowledge first in the Refreshers section.


For a quantum system, you cannot make a multipole expansion in the same way as you would do it for a classical system. The difference is that you will need perturbation theory in the quantum case. This video explains why and how:

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Answer two questions about this video:
  • Describe the complications you would run into if you would try to use perturbation theory to study a system with a nucleus of general shape without having made a multipole expansion first. Put your answer in the ‘post first’ forum underneath. As usual, feel free to comment respectfully on the answers of your colleagues.
  • You know that using a multipole expansion (and truncating it) is an approximation to reality. (1) When is it valid? You also know that using perturbation theory (up to first order) is an approximation to reality. (2) When is it valid? Eventually, (3) is it feasible to realize simultaneously the conditions required for the truncated multipole expansion as well as perturbation theory up to a given order to be valid, for a system of interacting nuclei and electrons? Put your ansers to (1), (2) and (3) in the form underneath. It will be discussed in the upcoming feedback webinar.
The ‘post first’ forum for the first task :

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The form with the three questions for the second task :