PERTURBATIVE AND VARIATIONAL CALCULATIONS OF CHARGE FLUCTUATIONS OF AN EXTENDED HUBBARD-MODEL

A charge-transfer instability that occurs in an extended Hubbard model with strong nearest-neighbor repulsions is examined nonperturbatively using variational wave functions. We show that a single mode approximation applied to a Hartree-Fock wave function accurately reproduces previous weak-coupling results on excitonic spectra. We then apply the method to a Gutzwiller variational wave function and extract information about the dynamic charge fluctuations in the intermediate and strong-coupling regimes. © 1990 The American Physical Society.