Linear response formula for open systems

TL;DR

This paper derives an exact formula for the finite frequency response of open classical systems connected to reservoirs, valid for any conserved current and applicable at non-zero frequencies without relying on traditional Green-Kubo relations.

Contribution

It provides a novel, exact response formula for open systems at finite frequencies, extending beyond standard Green-Kubo approaches.

Findings

Exact response expression involving boundary current correlations

Valid for any conserved current in open systems

Applicable at non-zero frequencies without additional assumptions

Abstract

An exact expression for the finite frequency response of open classical systems coupled to reservoirs is obtained. The result is valid for any conserved current. No assumption is made about the reservoirs apart from thermodynamic equilibrium. At non-zero frequencies, the expression involves correlation functions of boundary currents and cannot be put in the standard Green-Kubo form involving currents inside the system.