Relation between occupation in the first coordination shells and Widom line in Core-Softened Potentials

TL;DR

This study investigates how the structure of core-softened potentials influences density and diffusion anomalies, linking the Widom line to the equality of radial distribution functions at different scales.

Contribution

It reveals how the slope and range of potential features affect anomalous regions and connects structural changes to the Widom line in core-softened systems.

Findings

Anomalous regions expand with decreasing slope and range of potential features.

Density anomalies correlate with non-monotonic radial distribution functions.

Widom line corresponds to equal radial distribution functions at two scales.

Abstract

Three core-softened families of potentials are checked for the presence of density and diffusion anomalies. These potentials exhibit a repulsive core with a softening region and at larger distances an attractive well. We found that the region in the pressure-temperature phase diagram in which the anomalies are present increases if the slope between the core-softened scale and the attractive part of the potential decreases. The anomalous region also increases if the range of the core-softened or of the attractive part of the potential decreases. We also show that the presence of the density anomaly is consistent with the non monotonic changes of the radial distribution function at each one of the two scales when temperature and density are varied. Then, using this anomalous behavior of the structure we show that the pressures and the temperatures in which the radial distribution functions of the two length scales are equal are identified with the Widom line.