Krylov-space approach to the equilibrium and the nonequilibrium single-particle Green's function

Abstract

The zero-temperature single-particle Green's function of correlated fermion models with moderately large Hilbert-space dimensions can be calculated by means of Krylov-space techniques. The conventional Lanczos approach consists of finding the ground state in a first step, followed by an approximation for the resolvent of the Hamiltonian in a second step. We analyze the character of this approximation and discuss a numerically exact variant of the Lanczos method which is formulated in the time domain. This method is extended to get the nonequilibrium single-particle Green's function defined on the Keldysh-Matsubara contour in the complex time plane. The proposed method will be important as an exact-diagonalization solver in the context of self-consistent or variational cluster-embedding schemes. For the recently developed nonequilibrium cluster-perturbation theory, we discuss the efficient implementation and demonstrate the feasibility of the Krylov-based solver. The dissipation of a strong local magnetic excitation into a non-interacting bath is considered as an example for applications.

20 pages, 5 figures, v2 with minor corrections, JPCM in press

References in corpus (7)

• Continuous-time Monte Carlo methods for quantum impurity models
• Dynamical phase transition in correlated fermionic lattice systems
• Variational cluster approach to correlated electron systems in low dimensions
• Variational cluster approach to spontaneous symmetry breaking: The itinerant antiferromagnet in two dimensions
• High-order commutator-free exponential time-propagation of driven quantum systems
• Time evolution of one-dimensional Quantum Many Body Systems
• Non-equilibrium cluster-perturbation theory

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