Hartree-Fock study of electronic ferroelectricity in the Falicov-Kimball   model with $f$-$f$ hopping
  The Hartree-Fock (HF) approximation with the charge-density-wave (CDW) instability is used to study the ground-state phase diagram of the spinless Falicov-Kimball model (FKM) extended by $f$-$f$ hopping in two and three dimensions. It is shown that the HF solutions with the CDW instability reproduce perfectly the two-dimensional intermediate coupling phase diagram of the FKM model with $f$-$f$ hopping calculated recently by constrained path Monte Carlo (CPMC) method. Using this fact we have extended our HF study on cases that have been not described by CPMC, and namely, (i) the case of small values of $f$-electron hopping integrals, (ii) the case of weak Coulomb interactions and (iii) the three-dimensional case. We have found that ferroelectricity remains robust with respect to the reducing strength of coupling ($f$-electron hopping) as well as with respect to the increasing dimension of the system. 
Pavol Farkasovsky