Abstract

Macroscopic properties of a system represent the responses of the system to external stimuli, i.e., its internal processes. Their prediction remains a key challenge in science. Based on the second law of thermodynamics, entropy drives all internal processes in systems. While the total entropy of a system can be accurately obtained by integration of experimentally measured heat capacity, its theoretical prediction remains elusive due to the difficulty in theoretically sampling all configurations in the system. Entropy of a system is counted theoretically by either statistical mechanics in terms of Gibbs distribution or quantum mechanics in terms of Fermi-Dirac and Bose Einstein distributions. Our newly termed zentropy theory integrates them into a nested formula to account for disorder and fluctuations from the electronic scale to the macroscopic scale of the system [1]. In this presentation, the zentropy theory is introduced through the combined law of thermodynamics containing entropy production due to internal processes, and its capability is demonstrated through prediction of emergent behaviors in magnetic and ferroelectric materials including singularity at critical points, effects previously thought to be explainable exclusively via strong correlated physics. Discussions in fundamental understanding and parameter-free prediction of the magnetic and ferroelectric properties will be given. Furthermore, the entropy production in the combined law enables us to derive flux equations and coefficients of cross-phenomena from fundamental thermodynamics [2].

[1] Liu, Z.-K., Wang, Y. & Shang, S.-L. Zentropy Theory for Positive and Negative Thermal Expansion. J. Phase Equilibria Diffus. (2022) doi:10.1007/s11669-022-00942-z.

[2] Liu, Z.-K. Theory of cross phenomena and their coefficients beyond Onsager theorem. Mater. Res. Lett. 10, 393–439 (2022).