Exact eigenstates of Hubbard models with and without bond–charge interactions on general graphs

Abstract We investigate Hubbard models with bond–charge interactions on general graphs. For a Hamiltonian H of such a model, we provide the condition on its parameters under which the η -pairing method can be employed to construct its exact eigenstates. We arrive at this condition by finding that the requirement for the η -pairing state ( η † ) N ∣ 0 〉 to be an eigenstate of H is identical to the requirement for it to be an eigenstate of a Hubbard-type Hamiltonian H m without bond–charge interactions. When the condition for ( η † ) N ∣ 0 〉 to be an eigenstate of the Hubbard-type Hamiltonian H m is satisfied, we demonstrate that there are additional states, distinct from ( η † ) N ∣ 0 〉 , which are also exact eigenstates of H m . Our results enhance the understanding of Hubbard models on general graphs, both with and without bond–charge interactions.