Multiconfiguration time-dependent Hartree impurity solver for nonequilibrium dynamical mean-field theory

TL;DR

This paper introduces a multiconfiguration time-dependent Hartree (MCTDH) impurity solver for nonequilibrium dynamical mean-field theory, enabling efficient simulation of large bath systems and long-time dynamics in correlated lattice models.

Contribution

The authors develop and demonstrate the use of MCTDH as an impurity solver in nonequilibrium DMFT, outperforming exact diagonalization for large baths and extending simulation capabilities.

Findings

MCTDH outperforms exact diagonalization for large baths.

MCTDH enables simulation of longer times in nonequilibrium DMFT.

Self-consistent two-time impurity Green's functions can be computed with MCTDH.

Abstract

Nonequilibrium dynamical mean-field theory (DMFT) solves correlated lattice models by obtaining their local correlation functions from an effective model consisting of a single impurity in a self-consistently determined bath. The recently developed mapping of this impurity problem from the Keldysh time contour onto a time-dependent single-impurity Anderson model (SIAM) [C. Gramsch et al., Phys. Rev. B 88, 235106 (2013)] allows one to use wave function-based methods in the context of nonequilibrium DMFT. Within this mapping, long times in the DMFT simulation become accessible by an increasing number of bath orbitals, which requires efficient representations of the time-dependent SIAM wave function. These can be achieved by the multiconfiguration time-dependent Hartree (MCTDH) method and its multi-layer extensions. We find that MCTDH outperforms exact diagonalization for large baths in which the latter approach is still within reach and allows for the calculation of SIAMs beyond the system size accessible by exact diagonalization. Moreover, we illustrate the computation of the self-consistent two-time impurity Green's function within the MCTDH second quantization representation.