Computation of the equilibrium three-particle entropy for dense atomic fluids by molecular dynamics simulation

Area of Science:

• Thermodynamics
• Statistical Mechanics
• Computational Physics

Background:

• Understanding the entropy of fluids is crucial for predicting their thermodynamic properties.
• Previous studies on Lennard-Jones systems provide a basis for comparison.
• The Weeks-Chandler-Andersen (WCA) model is a simplified potential used to study fluid behavior.

Purpose of the Study:

• To compute the two- and three-particle contributions to the entropy of a WCA fluid.
• To investigate a new method for calculating three-particle correlation functions and entropy.
• To analyze numerical instabilities and errors in entropy calculations.

Main Methods:

• Molecular dynamics simulations were employed to model the WCA fluid.
• A novel method was utilized for computing the three-particle correlation function and entropy.
• Extrapolation procedures and careful bin size selection were used to address statistical and discretization errors.

Main Results:

• Results for the WCA fluid were qualitatively similar to those observed in Lennard-Jones systems.
• A numerical instability was identified in the three-particle entropy calculation, likely intrinsic to the method.
• The magnitude of the three-particle contribution increases significantly as the fluid approaches freezing.

Conclusions:

• A new method for computing three-particle entropy contributions in WCA fluids is presented.
• Despite the increase in three-particle entropy near freezing, approximating excess entropy with only two-body terms may be less error-prone due to overestimation issues.
• Careful selection of bin size is essential for accurate three-particle entropy estimation, even near the freezing point.