Configurational temperature in active matter. II. Quantifying the deviation from thermal equilibrium

Area of Science:

• Statistical Mechanics
• Soft Matter Physics
• Computational Physics

Background:

• Active matter systems exhibit complex behaviors not fully described by equilibrium thermodynamics.
• Quantifying the deviation from thermal equilibrium in these systems is crucial for understanding their unique properties.

Purpose of the Study:

• To propose and validate a new metric, the ratio of systemic temperature (Ts) to configurational temperature (Tconf), for quantifying the departure from thermal equilibrium in active matter.
• To demonstrate the computational efficiency and broad applicability of this metric.

Main Methods:

• Calculating the ratio Ts/Tconf, where Ts is the canonical-ensemble temperature and Tconf is a local temperature derived from potential energy variations.
• Utilizing equilibrium simulations combined with a single steady-state active-matter configuration.
• Analyzing radial distribution functions and phase behavior in 3D Kob-Andersen and 2D Yukawa models with active Ornstein-Uhlenbeck and active Brownian Particle dynamics.

Main Results:

• The Ts/Tconf ratio effectively quantifies the deviation from thermal equilibrium across different active matter models.
• Ts/Tconf, along with structural and dynamic properties, remains invariant along the motility-induced phase separation boundary in the 2D Yukawa model.
• The metric is shown to be applicable to driven Hamiltonian systems beyond active matter.

Conclusions:

• The Ts/Tconf ratio provides a robust and computationally accessible measure of non-equilibrium in active matter.
• This metric offers insights into the phase behavior and dynamics of active systems.
• The proposed method generalizes to a wider range of systems with potential-energy functions, facilitating non-equilibrium studies.