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In connection with the study of the extended Hubbard model on an isosceles triangular cluster, we discovered a factor two error in the coding of the Ising part of the Heisenberg term in the Hamiltonian.  In consequence the rigorous results remain valid, but not for the isotropic Heisenberg model, but for an anisotropic Heisenberg model.

Rigorous solution of a Hubbard model extended by nearest‐neighbour Coulomb and isotropic exchange interaction on a triangle and tetrahedron