Charge order in the extended Hubbard model

Magnetic and charge order in half-filled and doped finite two-dimensional (8 x 8) clusters described by the extended Hubbard Hamiltonian with medium to large on-site (U) and intersite (V) Coulomb repulsion were investigated using correlated wavefunctions. The treatment of spatially inhomogeneous correlations was possible thanks to a combination of the local ansatz and the local increments expansion methods. The surprising result is that in the half-filled case the correlations do not influence the transition from the antiferromagnetic (AF) to charge order (CO) phase found in the HartreeFock approximation. For the doped systems we found a variety of stripe or superlattice-like structures for small values of V, while for larger V we identified robust CO phases. For smaller doping (delta = 1/8 and 1/4) the charge-majority sublattice has typically inhomogeneous charge distribution and is decorated by various magnetic patterns, while for larger doping (delta = 1/2) the co-phase is homogeneous (ideal) and with superimposed AF order.