Gulacsi, Miklos2015-12-132015-12-130950-0839http://hdl.handle.net/1885/80423A new variational scheme based on a modified Bethe-Peierls method is used to study the ground state properties of the one-dimensional t-J model. Expectation values are evaluated by cutting out a four-site cluster from a correlated Fermi sea, the ground state of which is described by a variational trial wave function. We study a generalized Gutzwiller state where nearest-neighbour hole-hole correlations are controlled variationally. From the electron concentration dependence of the ground state energy, we determine the true thermodynamic boundary where segregation into an electron-rich, and purely hole phase sets in. We also determine the spinodal line and pair susceptibilities. The variational method is applied also to an extended t-J-V model, where V is the coupling constant of the charge interaction term.Keywords: Approximation theory; Electronic structure; Fermi level; Mathematical models; Maxwell equations; Phase separation; Statistical mechanics; Thermodynamics; Gutzwiller approximation; Thermodynamic limit; Wave functions; Ground state200410.1080/095008305123313250732015-12-11