Stability of the high-spin ground state in the Peierls-extended Hubbard model

Based on the Peierls-extended Hubbard model and breaking the alternative sy mmetry, we examine the stability of the high-spin ground state on a pi -con jugated hydrocarbon chain with respect to the intersite Coulomb interaction and dimerization of the backbone. We find that the ground state switches f rom a low-spin to a high-spin state only when the on-site Coulomb interacti on approaches a critical value. When increasing the intersite Coulomb inter action or dimerization, the ground state switches from a high-spin to a low -spin state. (C) 2001 American Institute of Physics.