Using the fluctuation-dissipation theorem for nonconservative forces
arXiv:1908.11287 · doi:10.1103/PhysRevResearch.1.033151
Abstract
An equilibrium system which is perturbed by an external potential relaxes to a new equilibrium state, a process obeying the fluctuation-dissipation theorem. In contrast, perturbing by nonconservative forces yields a nonequilibrium steady state, and the fluctuation-dissipation theorem can in general not be applied. Here we exploit a freedom inherent to linear response theory: Force fields which perform work that does not couple statistically to the considered observable can be added without changing the response. Using this freedom, we demonstrate that the fluctuation-dissipation theorem can be applied for certain nonconservative forces. We discuss the case of a nonconservative force field linear in particle coordinates, where the mentioned freedom can be formulated in terms of symmetries. In particular, for the case of shear, this yields a response formula, which we find advantageous over the known Green-Kubo relation in terms of statistical accuracy.
arXiv comment5 pages, 3 figures (v2: Acknowledgments have been extended. v3: minor changes in the abstract, text, and Fig. 3; Ref. [22] has been added)
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