Ground States of the Falicov-Kimball Model Extended by Nonlocal Coulomb Interactions

Abstract

The small-cluster exact-diagonalizations are used to study the ground states of the Falicov–Kimball model extended by nonlocal Coulomb interactions (the nearest-neighbour interaction Unn and the correlated hopping t ′). It is shown that the ground-state phase diagrams found for the conventional Falicov–Kimball model are strongly changed when the nonlocal interactions are added. This is illustrated for two selected values of the on-site Coulomb interaction (U) that represent typical behaviours of the model in the intermediate and strong coupling limit. A number of remarkable results are found. (i) The phase separation takes place for a wide range of Unn and t ′ in both interaction limits. (ii) New types of inhomogeneous charge ordering are observed for nonzero Unn and t ′. (iii) Depending on the values of Unn and t′, the model is able to describe both the continuous as well as discontinuous changes of the f -electron occupation number.