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Negative specific heats: where Clausius and Boltzmann entropies separate
Lander Bogers1, Faezeh Khodabandehlou1, Christian Maes1
1Department of Physics and Astronomy, KU Leuven, Belgium. christian.maes@kuleuven.be.
Physical Chemistry Chemical Physics : PCCP
|July 2, 2025
Summary
Steady nonequilibrium systems can exhibit negative heat capacities, a phenomenon explained by an anticorrelation between quasipotential and pseudopotential. This finding offers insights into thermal response in systems far from equilibrium.
Area of Science:
- Thermodynamics
- Statistical Mechanics
- Nonlinear Dynamics
Background:
- Steady nonequilibrium systems dissipate energy and generate excess heat during parameter changes.
- Negative heat capacities are common in nonequilibrium systems, unlike in equilibrium systems.
- Understanding thermal response in nonequilibrium states is crucial.
Purpose of the Study:
- To elucidate the origin of negative heat capacities in steady nonequilibrium systems.
- To illustrate this phenomenon using Markov models.
- To quantify the negative thermal response via effective temperatures.
Main Methods:
- Analysis of steady nonequilibrium systems in contact with a thermal bath.
- Utilizing Markov models to simulate system dynamics.
- Defining heat capacity as excess heat per degree temperature change.
Main Results:
- Identified negative heat capacities as a common feature of steady nonequilibrium systems.
- Demonstrated that negativity arises from an anticorrelation between quasipotential and pseudopotential.
- Showed that quasipotential relates to excess heat and Clausius entropy, while pseudopotential relates to Boltzmann entropy.
Conclusions:
- The negative thermal response in nonequilibrium systems is fundamentally linked to the interplay between different entropic measures.
- Markov models provide a tractable framework for studying these complex thermodynamic behaviors.
- The concept of effective temperatures can be used to quantify negative heat capacities.
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