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Perturbed TD-Hamiltonian

  1. Feb 13, 2016 #1
    Why does a time-dependent perturbed Hamiltonian commonly have diagonal elements equal to zero?
  2. jcsd
  3. Feb 17, 2016 #2


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    Staff: Mentor

    Because the perturbation is what is going to mix the eigenstates of the unperturbed Hamiltonian. But the diagonal elements could be non-zero: an actual physical perturbation could also shift the energy levels. Most often, it is easier to work with a perturbation that only mixes the states, so I would move the diagonal elements to the "unperturbed" Hamiltonian in such a case.
  4. Feb 17, 2016 #3
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