Liquid-A dynamic mixture of gas-like and solid-like states

CF Hou and QY Cao and W Ge, CHEMICAL PHYSICS, 595, 112725 (2025).

DOI: 10.1016/j.chemphys.2025.112725

From the classical thermodynamic view, the three matter phases of solid, liquid and gas are thermodynamic states in equilibrium, determined by the Gibbs free energy. Gases and solids have already been successfully described by some theories, however, the theory for liquids is elusive yet due to their complex dynamic features. Herein, this traditional issue is revisited and analyzed. The gas and solid phases are each regarded as a single thermodynamic state dominated by a single dominant mechanism, while the liquid phase is a mixed thermodynamic state with alternative domination of the gas-like and solid-like mechanisms. Taking simple argon fluid as a model system, the number density and total energy variations for the three phases with the system temperature are first reproduced by molecular dynamics simulation. Then, the compromise in competition between potential energy and kinetic energy in the system and their spatiotemporal variation are plotted. Furthermore, a well- defined gas-like fraction for liquids is presented to precisely calculate some thermodynamic and structural quantities such as total energy, heat capacity and radial distribution function.

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