Structure of liquids from reference hard body fluids: Additive vs non-additive hard body models

Area of Science:

• Thermodynamics
• Statistical Mechanics
• Physical Chemistry

Background:

• Hard body fluids are commonly used as reference systems in molecular-based equations of state for simple liquids.
• Direct application of hard body models to polar and associating fluids has been limited due to their complex interactions.
• Site-site interactions in hard body models can lead to non-additivity, affecting structural properties.

Purpose of the Study:

• To analyze the effect of non-additivity on structural and orientation correlations in polar and associating fluids.
• To investigate the applicability of non-additive hard body models as reference systems for complex liquids.
• To compare the structural properties of non-additive hard body models with empirical models of real fluids.

Main Methods:

• Molecular simulations were used to model fused-hard-sphere bodies.
• Analysis of site-site and dipole-dipole correlation functions.
• Comparison of non-additive hard body models with empirical models for carbon dioxide, acetonitrile, acetone, methanol, and water.

Main Results:

• Non-additivity in hard body models significantly modifies structural and orientation correlations.
• The structure of non-additive purely repulsive hard body models shows surprising similarities to empirical models of real polar and associating liquids.
• Differences in mutual geometry within non-additive models impact correlation functions.

Conclusions:

• Non-additive hard body models provide a valuable framework for understanding the structure of polar and associating fluids.
• The findings extend the potential application of hard body fluids as reference systems in perturbation theories.
• This research bridges the gap between simple hard body models and complex real fluid behavior.