This paper presents a renormalization approach to many-particle systems. By
starting from a bare Hamiltonian H=H0+H1 with an
unperturbed part H0 and a perturbation H1,we define an
effective Hamiltonian which has a band-diagonal shape with respect to the
eigenbasis of H0. This means that all transition matrix elements are
suppressed which have energy differences larger than a given cutoff λ
that is smaller than the cutoff Λ of the original Hamiltonian. This
property resembles a recent flow equation approach on the basis of continuous
unitary transformations. For demonstration of the method we discuss an exact
solvable model, as well as the Anderson-lattice model where the well-known
quasiparticle behavior of heavy fermions is derived.Comment: 11 pages, final version, to be published in Phys. Rev.