Renormalization group approach to self-consistent-field approximation for the interacting electrons

Due to the retarded nature of the phonon-mediated electron-electron interac tion, neither fast Fourier transform (FFT) nor previously developed NRG met hods for Hubbard-type purely electronic models are applicable, while brute- force solutions are limited by the demands on computational time and storag e which increase rapidly at low temperature T. A new numerical renormalizat ion group (NRG) approach to the solution of self-consistent-field equations for correlated lattice electrons is illustrated for the two-dimensional Hu bbard-type model. This approach allows us to handle the fermion frequency m atrix inversions in the FLEX equations efficiently. Several orders of magni tude of CPU time and storage can be saved at the temperature scales relevan t to electronic phase transitions.