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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

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# A Difference between Hubbard and Heisenberg-model

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