Charge-ordering in quarter-filled low-dimensional conductors: implications of long-range Coulomb interactions

Abstract

We investigate the charge-ordering (CO) in quasi one-dimensional Pariser-Parr-Pople model at quarter filling where the longer-range Coulomb interactions and dimerization in the hopping integrals are included. The intersite electron repulsion integrals have been incorporated using the interpolation formulae given by Ohno. We find that while the longer-range interactions stabilize the CO phase, dimerization suppresses its stability. Using an exact diagonalization scheme for small cluster sizes, we determine the zero-temperature charge-ordering phase boundary in the model parameter space. The realistic parameter values for the low-dimensional Bechgaard salts are found to exist within the CO phase boundary. We conjecture that the true longer-range electron-electron interactions are necessary to account for the CO phase in these organic systems.