Eur. Phys. J. B 5, 605-611 (1998)
https://doi.org/10.1007/s100510050485

Flow equations for band-matrices^*

Institut für Theoretische Physik, Ruprecht-Karls-Universität, Philosophenweg 19, 69120 Heidelberg, Germany

Corresponding author: ^a This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 2 February 1998
Accepted: 17 March 1998
Published online: 15 October 1998

Abstract

Continuous unitary transformations can be used to diagonalize or approximately diagonalize a given Hamiltonian. In the last four years, this method has been applied to a variety of models of condensed matter physics and field theory. With a new generator for the continuous unitary transformation proposed in this paper one can avoid some of the problems of former applications. General properties of the new generator are derived. It turns out that the new generator is especially useful for Hamiltonians with a banded structure. Two examples, the Lipkin model, and the spin-boson model are discussed in detail.