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A Difference between Hubbard and Heisenberg-model

  1. Jan 5, 2017 #1
    Hi,
    I read a chapter about the Heisenberg-model,
    and then something about the Hubbard-Model.
    The Heisenberg-model just shows, that neighbouring spins allign antiparallel if J<0.
    The Hubbard-Model says, that there is a hopping probability t and an Coulomb replsion,
    so that a material becomes metal or insulator.

    I read that for the Hubbard-Model J=2t^2/U, where does this come from?

    Thank you
     
  2. jcsd
  3. Jan 5, 2017 #2

    DrDu

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    Science Advisor

    The Heisenberg model can be viewed at as the large U limit of the Hubbard model. The states of lowest energy are those with the least number of double occupied sites. For these states, you can do a perturbation expansion in 1/U to get J.
     
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