Variational solution of the one-dimensional t-J model

A 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.