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Static and dynamic anomalies in a repulsive spherical ramp liquid: theory and simulation
Pradeep Kumar1, Sergey V Buldyrev, Francesco Sciortino
1Center for Polymer Studies and Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
Summary
This study models liquid anomalies like water's expansion upon cooling using a repulsive ramp potential. Theoretical and simulation results confirm structural anomalies and dynamics controlled by liquid structure.
Area of Science:
- Condensed matter physics
- Computational physics
- Statistical mechanics
Background:
- Liquid water exhibits anomalous behavior, including expansion upon cooling and increased diffusivity under compression.
- Understanding these anomalies is crucial for developing accurate models of liquid systems.
Purpose of the Study:
- To investigate static and dynamic properties of a model system with a repulsive ramp potential.
- To compare theoretical predictions with simulation results for systems exhibiting water-like anomalies.
- To explore the relationship between liquid structure and dynamics.
Main Methods:
- Simulations of particles interacting via a spherically symmetric repulsive ramp potential.
- Calculation of thermodynamic state points (P(rho,T)) using both simulation and the Rogers-Young (RY) closure for the Ornstein-Zernike (OZ) equation.
- Analysis of dynamic properties, including diffusivity and structural changes.
Main Results:
- The model successfully reproduces anomalies similar to those in liquid water, such as expansion upon cooling.
- Theoretical and simulation results for state points P(rho,T) show good agreement.
- Evidence of a line of isobaric density maxima, compressibility minima/maxima, and a potential liquid-liquid critical point was found.
- Dynamic properties exhibit nonmonotonic behavior, alternating between slowing down and speeding up with increasing density, linked to structural changes.
- Mode coupling theory accurately predicts these dynamic anomalies and multiple glass phases, confirming structure's control over dynamics.
Conclusions:
- The repulsive ramp potential model effectively captures key anomalies observed in liquid water.
- The study validates the predictive power of mode coupling theory in relating liquid structure to dynamics.
- Structural rearrangements are identified as the primary driver of the observed dynamic anomalies in this model system.
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