International Journal of Modern Physics B f c World Scientic Publishing Company RENORMALIZATION GROUP APPROACHES TO STRONGLY CORRELATED ELECTRON SYSTEMS

In recent years the numerical renormalization group method NRG has been extended to the calculation of dynamic response functions and transport properties of magnetic impurity models The approach can now be applied more widely to lattice models of strongly correlated electron systems by the use of dynamical mean eld theory DMFT in which the lattice problem is transformed into one for an eective impurity with an additional self consistency constraint We review these developments and assess the potential for further applications of this approach We also discuss an alternative approach to renormalization renormalized perturba tion theory in which the leading asymptotically exact results for the low temperature regime for a number of magnetic impurity models can be obtained within nite order perturbation theor