Static and Dynamic Anomalies in a Repulsive Spherical Ramp Liquid: Theory and Simulation

TL;DR

This paper investigates static and dynamic anomalies in a repulsive spherical ramp liquid through theory and simulation, revealing water-like behaviors, phase diagram features, and the predictive power of mode coupling theory.

Contribution

It provides a comprehensive comparison of theoretical and simulation results for a ramp potential model, highlighting anomalies and confirming mode coupling theory's predictions.

Findings

Presence of density maxima and compressibility anomalies

Evidence of a liquid-liquid critical point

Mode coupling theory accurately predicts dynamic anomalies

Abstract

We compare theoretical and simulation results for static and dynamic properties for a model of particles interacting via a spherically symmetric repulsive ramp potential. The model displays anomalies similar to those found in liquid water, namely, expansion upon cooling and an increase of diffusivity upon compression. In particular, we calculate the phase diagram from the simulation and successfully compare it with the phase diagram obtained using the Rogers-Young (RY) closure for the Ornstein-Zernike equation. Both the theoretical and the numerical calculations confirm the presence of a line of isobaric density maxima, and lines of compressibility minima and maxima. Indirect evidence of a liquid-liquid critical point is found. Dynamic properties also show anomalies. Along constant temperature paths, as the density increases, the dynamics alternates several times between slowing down and speeding up, and we associate this behavior with the progressive structuring and de-structuring of the liquid. Finally we confirm that mode coupling theory successfully predicts the non-monotonic behavior of dynamics and the presence of multiple glass phases, providing strong evidence that structure (the only input of mode coupling theory) controls dynamics.