The Hubbard transition in molecular systems

The Hubbard transition occurring in molecular systems is investigated by exact diagonalization of the Hubbard model for a set of planar eight-atom systems. The symmetry distortion observed in pentalene has been attributed to the Hubbard transition. Two novel systems are first found to have double transitions in their ground states as the Hubbard parameters vary, confirming that there exists another novel picture of the Hubbard transition in molecular systems.