Perturbative and nonperturbative parts of eigenstates and local spectral density of states: The Wigner-band random-matrix model

The Wigner-band random-matrix model is studied by making use of a generaliz ation of Brillouin-Wigner perturbation theory. Energy eigenfunctions are sh own to be divided into perturbative and nonperturbative parts. Several pert urbation strengths predicted by the perturbation theory are found to pray i mportant roles in the variation of the shape of the local spectral density of states with perturbation strength.