Polaron band formation in the Holstein model

We present numerical exact results for the polaronic band structure of the Holstein molecular crystal model in one and two dimensions. The use of a direct Lanczos diagonalization technique, preserving the full dynamics and quantum nature of phonons, allows us to analyze in detail the renormalization of both quasiparticle bandwidth and dispersion by the electron-phonon interaction. For the two-dimensional case some of our exact data are compared with the results obtained in the framework of a recently developed finite-cluster strong-coupling perturbation theory.