Sum-rule Conserving Spectral Functions from the Numerical Renormalization Group

Abstract

We show how spectral functions for quantum impurity models can be calculated very accurately using a complete set of ``discarded'' numerical renormalization group eigenstates, recently introduced by Anders and Schiller. The only approximation is to judiciously exploit energy scale separation. Our derivation avoids both the overcounting ambiguities and the single-shell approximation for the equilibrium density matrix prevalent in current methods, ensuring that relevant sum rules hold rigorously and spectral features at energies below the temperature can be described accurately.

4 pages + 1 page appendix, 2 figures

References in corpus (4)

• Real-time dynamics in Quantum Impurity Systems: A Time-dependent Numerical Renormalization Group Approach
• Numerical Renormalization Group for Bosonic Systems and Application to the Subohmic Spin-Boson Model
• A Numerical Renormalization Group approach to Green's Functions for Quantum Impurity Models
• Spin Precession and Real Time Dynamics in the Kondo Model: A Time-Dependent Numerical Renormalization-Group Study

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