Density-matrix renormalization-group method in momentum space
  A momentum-space approach of the density-matrix renormalization-group (DMRG) method is developed. Ground state energies of the Hubbard model are evaluated using this method and compared with exact diagonalization as well as quantum Monte-Carlo results. It is shown that the momentum-space DMRG is a very useful numerical tool for studying the Hubbard model and other fundamental models of interacting electrons in two dimensions. For the Hubbard model in two dimensions, the momentum-space DMRG method reproduces accurately the exact diagonalization results of ground state energies on a $4\times 4$ lattice and yields new upper bounds of ground state energies on an 8$\times$8 lattice. 
T. Xiang