Comment on "On the unphysical solutions of the Kadanoff--Baym equations in linear response: Correlation-induced homogeneous density-distribution and attractors"

TL;DR

This paper refutes claims that the Kadanoff--Baym equations inherently lead to unphysical homogeneous densities and damping, demonstrating that previous results were due to numerical inaccuracies rather than fundamental issues.

Contribution

The authors provide accurate solutions to the KBE, showing that the predicted unphysical attractors and damping are artifacts of numerical errors, not intrinsic properties.

Findings

The supposed universal attractor does not exist in accurate solutions.

Numerical inaccuracies caused the previously reported unphysical results.

Mean-field dynamics are not necessarily damped as previously conjectured.

Abstract

In a recent Rapid Communication [A. Stan, Phys. Rev. B \textbf{93}, 041103(R) (2016)], the reliability of the Keldysh--Kadanoff--Baym equations (KBE) using correlated selfenergy approximations applied to linear and nonlinear response has been questioned. In particular, the existence of a universal attractor has been predicted that would drive the dynamics of any correlated system towards an unphysical homogeneous density distribution regardless of the system type, the interaction and the many-body approximation. Moreover, it was conjectured that even the mean-field dynamics would be damped. Here, by performing accurate solutions of the KBE for situations studied in that paper, we prove these claims wrong being caused by numerical inaccuracies.