  We propose a density matrix renormalization group approach to tackle a
two-state system coupled to a bosonic bath with continuous spectrum. In this
approach, the optimized phonon scheme is applied to several hundred phonon
modes which are divided linearly among the spectrum. Although DMRG cannot
resolve very small energy scales, the delocalized-localized transition points
of the two-state system are extracted by the extrapolation of the flow diagram
results. The phase diagram is compared with the numerical renormalization group
results and shows good agreement in both Ohmic and sub-Ohmic cases.
