Density-matrix renormalization-group method for excited states

The density-matrix renormalization-group (DMRG) method can provide approxim ate ground-state wave functions for many one-dimensional systems with a hig h degree of accuracy. Conventional DMRG techniques, however, cannot be expe cted to give accurate excited-state information because the excited states of interest are not explicitly included in the calculations. We discuss tec hniques for extending DMRG to accurately target and investigate arbitrary e xcited states. As an example we apply the method to investigate the propert ies of excitons within the extended Hubbard model. Our results show that ex cited-state calculations within the standard DMRG procedure give results th at are quantitatively incorrect. [S0163-1829(99)11715-6].