Microscopic View of Heat Capacity of Matter

In contrast to thermodynamic properties of solids and gases that are often described by phonon quasi-particles and real particles, respectively, our microscopic understanding of thermodynamics in liquids is lacking due to strong atomic interactions and lack of symmetry. Recent prior works have initiated efforts to understand heat capacity of liquids based on phonon quasi-particles similar to that of solids but often rely on free fitting parameters and questionable assumptions. In this work, we perform instantaneous normal mode and velocity autocorrelation analysis on single element systems under various conditions up to 10⁷ K and 1 TPa. Our results suggest that heat capacity of liquids can be expressed by a combination of both quasi-particles and real-particles, leading to a unified framework to describe heat capacity of all three phases of matter: solid, liquid, and gas.<br/><br/>*Supported by the Department of Energy, Office of Science, Basic Energy Sciences,Materials Sciences and Engineering Division.