Thermodynamic properties of extended Hubbard chains

In this contribution we discuss the thermodynamic behaviour of Hubbard chains with an additional site-diagonal interaction. It is shown rigorously that the strong coupling limit is equivalent to a generalized anisotropic Heisenberg system, which in some recently discussed limiting cases degenerates to an Ising orX-Y system. The whole procedure also works for a collection of chains with interchain interaction, thus it is not restricted to strictly one-dimensional systems. The effect of a magnetic field is discussed, and the results are compared with a recent perturbation approach by using numerical results for the anisotropic Heisenberg chain.