Core-Softened System With Attraction: Trajectory Dependence of Anomalous Behavior

TL;DR

This study uses molecular dynamics to explore how water-like anomalies in a core-softened system depend on the thermodynamic trajectory, revealing that anomalies are trajectory-dependent and that Rosenfeld scaling validity varies accordingly.

Contribution

It demonstrates the trajectory dependence of water-like anomalies and the Rosenfeld entropy scaling relations in a core-softened system, highlighting the importance of analyzing multiple paths in phase space.

Findings

Anomalies depend on the thermodynamic path taken.

Diffusion and structural anomalies appear along isotherms but not isochores or isobars.

Rosenfeld scaling validity varies with the trajectory in phase space.

Abstract

In the present article we carry out a molecular dynamics study of the core-softened system and show that the existence of the water-like anomalies in this system depends on the trajectory in $P-\rho-T$ space along which the behavior of the system is studied. For example, diffusion and structural anomalies are visible along isotherms as a function of density, but disappears along the isochores and isobars as a function of temperature. On the other hand, the diffusion anomaly may be seen along adiabats as a function of temperature, density and pressure. It should be noted that it may be no signature of a particular anomaly along a particular trajectory, but the anomalous region for that particular anomaly can be defined when all possible trajectories in the same space are examined (for example, signature of diffusion anomaly is evident through the crossing of different isochors. However, there is no signature of diffusion anomaly along a particular isochor). We also analyze the applicability of the Rosenfeld entropy scaling relations to this system in the regions with the water-like anomalies. It is shown that the validity of the Rosenfeld scaling relation for the diffusion coefficient also depends on the trajectory in the $P-\rho-T$ space along which the kinetic coefficients and the excess entropy are calculated.