SYMMETRIZED DENSITY-MATRIX RENORMALIZATION-GROUP METHOD FOR EXCITED-STATES OF HUBBARD MODELS

We extend the density-matrix renormalization-group (DMRG) method to ex ploit parity, C-2 (rotation by pi) and electron-hole symmetries of mod el Hamiltonians. We demonstrate the power of this method by obtaining the lowest-energy stares in all eight symmetry subspaces of Hubbard ch ains with up to 50 sites. The ground-state energy, optical gap, and sp in gap of regular U=4t and U=6t Hubbard chains agree very well with ex act results. This development extends the scope of the DMRG method and allows future applications to study of optical properties of low-dime nsional conjugated polymeric systems.