Widom delta of supercritical gas-liquid coexistence

TL;DR

This paper introduces the concept of the 'Widom delta' in supercritical fluids, describing a region where liquid-like and gas-like structures coexist and transition smoothly, providing a microscopic understanding of supercritical behavior.

Contribution

It defines the Widom delta as a coexistence region in supercritical fluids and uses machine learning to analyze the continuous transition between liquid-like and gas-like states.

Findings

Identification of the Widom delta region in supercritical fluids

Machine learning reveals a continuous transition between states

Fluctuations between liquid-like and gas-like structures explain anomalous behavior

Abstract

We report on the coexistence of liquid-like and gas-like structures in supercritical fluid (SCF). The deltoid coexistence region encloses the Widom line, and may therefore be termed the "Widom delta". Machine learning analysis of simulation data shows continuous transition across the delta, from liquid-like to gas-like states, with fractions following a simplified two-state model. This suggests a microscopic view of the SCF as a mixture of liquid-like and gas-like structures, where the anomalous behavior near the critical point originates from fluctuations between the two types.