Microstructure and hydrogen bonding in water-acetonitrile mixtures

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Materials Science

Background:

• Microheterogeneity in liquid mixtures is significantly influenced by hydrogen bonding.
• Accurate molecular models are crucial for simulating the behavior of water-acetonitrile mixtures.

Purpose of the Study:

• To examine the role of water-acetonitrile hydrogen bonding in liquid mixture microheterogeneity.
• To evaluate and identify reliable molecular models for simulating water-acetonitrile systems.

Main Methods:

• NPT molecular dynamics simulations were performed for mixtures of six rigid, three-site acetonitrile models and one SPC/E water model.
• Model performance was assessed by comparing simulated liquid density and hydrogen bonding estimates (from Raman scattering and NMR relaxation) with experimental data.
• Self-diffusion coefficients of liquid acetonitrile were used for final model validation.

Main Results:

• Only the TraPPE-UA acetonitrile model accurately reproduced both liquid density and experimental hydrogen bonding estimates.
• Modifications to other acetonitrile models partially improved hydrogen bonding predictions, but often failed to accurately predict density.
• The self-diffusion coefficient further distinguished between the successful unmodified model and modified models.

Conclusions:

• The unmodified TraPPE-UA model is provisionally recommended for accurate simulations of water-acetonitrile mixtures.
• Careful selection and validation of molecular models are essential for reliable computational studies of liquid mixtures.