Issue 28, 2025

Negative specific heats: where Clausius and Boltzmann entropies separate

Abstract

Steady nonequilibria dissipate energy and, when changing external parameters, an extra or excess heat accompanies the relaxation to the new nonequilibrium condition. For nonequilibrium systems in contact with a thermal bath, the heat capacity is defined as that excess heat per degree temperature for a quasistatic change of the bath temperature. It is fairly common to find negative heat capacities for steady nonequilibrium systems, in contrast with the situation for systems in thermal equilibrium. We discuss and illustrate the origin of that negative thermal response using Markov models. We find that the negativity results from an anticorrelation between quasipotential and (a change in) pseudopotential, the first measuring (excess) heat (and Clausius entropy), and the latter being related to the Boltzmann entropy. It can be quantified via an appropriate choice of effective temperatures.

Graphical abstract: Negative specific heats: where Clausius and Boltzmann entropies separate

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Article information

Article type
Paper
Submitted
02 Apr 2025
Accepted
10 Jun 2025
First published
23 Jun 2025
This article is Open Access
Creative Commons BY-NC license

Phys. Chem. Chem. Phys., 2025,27, 15009-15023

Negative specific heats: where Clausius and Boltzmann entropies separate

L. Bogers, F. Khodabandehlou and C. Maes, Phys. Chem. Chem. Phys., 2025, 27, 15009 DOI: 10.1039/D5CP01269D

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