How Long-Range Are Three-Body "Exchange" Interactions in Liquid Water?

Area of Science:

• Computational chemistry
• Physical chemistry
• Molecular modeling

Background:

• Three-body interactions are vital for accurate water modeling, comprising polarization and exchange terms.
• Exchange interactions are complex, often damped or truncated due to computational cost (N^3 scaling) and fitting challenges.
• Current models often simplify or omit long-range three-body exchange effects.

Purpose of the Study:

• To investigate the impact of long-range three-body exchange interactions on water simulations.
• To determine which properties of water are sensitive to these specific interactions.
• To provide insights into discrepancies between theoretical and experimental water density data.

Main Methods:

• Systematically extending the average intermolecular separation (R_ab) of included trimers in simulations.
• Utilizing symmetry-adapted perturbation theory for rationalizing findings.
• Comparing simulation results with and without extended long-range three-body exchange interactions.

Main Results:

• Long-range three-body exchange interactions are crucial for accurately predicting liquid water density (ρ(T)) across temperatures.
• These effects are negligible for most other water properties.
• Non-polarization three-body effects decay as 1/R_ab^n at large separations, not exponentially, impacting water structure and density significantly due to anisotropy.

Conclusions:

• High-accuracy water models must incorporate long-range three-body exchange interactions, particularly for density predictions.
• The anisotropy of these interactions is key to their strong influence on liquid water's temperature-dependent density.
• This study helps resolve theoretical-experimental discrepancies in water density.