An alternative approach to the phonon theory of liquids: Evolution of the energy of diffusion

TL;DR

This paper introduces an alternative phonon theory for liquids that accounts for oscillating and diffusing atoms, providing new formulas for liquid energy and validating them against experimental data.

Contribution

It proposes a novel approach to liquid energy calculation by considering atom dynamics instead of the virial theorem, advancing the theoretical understanding of liquids.

Findings

Derived new formulas for liquid energy in quantum and classical cases

Validated predictions against experimental specific heat of liquid mercury

Presented a new expression for supercritical system energy

Abstract

With regard to the three basic states of matter (solid, liquid, gas), the calculation of the heat capacity of liquids in a general form has been considered one of the deepest and most interesting challenges in condensed matter physics, due to the strong, system-specific interactions involved. Notwithstanding the theoretical difficulties, there have recently been significant advances in our understanding of liquids, and the phonon theory of liquids has been proposed. However, this theory uses the virial theorem to calculate the liquid energy. Here, we propose an alternative version of the phonon theory of liquids by taking into account the numbers of oscillating atoms and diffusing atoms, rather than using the virial theorem. A new formula is derived for the liquid energy in both the quantum and the classical anharmonic cases. To verify the proposed approach, theoretical predictions are compared with the experimental specific heat of liquid mercury. Finally, we obtain a new expression for the energy of a supercritical system.