We show how to construct SO(4) invariant functions for strongly correlated Fermi systems on lattices of finite sizes. We illustrate the method on the case of the 1D Hubbard chain with four and with six sites.
A general method to construct basis functions for fermionic systems which account for the SU(2) symmetry and for the translational invariance of the Hamiltonian is presented. The method does not depend on the dimensionality of the system and it appears as a natural generalization of the Bethe Ansatz to the case of non integrable systems. As an example we present the block diagonalization of the Hubbard hamiltonian for finite number of sites in one and two dimensions.
We present a method for the simultaneous implementation of the spin symmetry, the pseudospin symmetry and the translational invariance in models for correlated electron systems on finite-size clusters. The application of this method leads to a significative reduction of the size of the Hamiltonian matrix blocks, thus considerably simplifying the diagonalization procedure. We illustrate the method solving exactly the Hubbard model on a 8-site chain in the Hilbert subspaces labelled by the eigenvalues of the spin, the pseudospin and the momentum operators. Some relevant thermodynamical quantities, such as the specific heat and the static magnetic susceptibility, are then evaluated and a brief discussion on the tendency of the model to exhibit ferromagnetism is also presented.
We present a method to compute eigenstates and eigenvalues of strongly correlated models on clusters. The calculation is performed applying the SU(2) symmetry, which allows a considerable reduction of the dimension of Hilbert space of the system. We illustrate the method classifying the states of the four-sites Hubbard model on a chain. This classification has been made using also the translational symmetry and the S\ifmmode \tilde{}\else \~{}\fi{}\ifmmode \tilde{U}\else \~{U}\fi{}(2) pseudospin symmetry. \textcopyright{} 1996 The American Physical Society.