A new united atom force field for alkylamines

Area of Science:

• Computational Chemistry
• Molecular Modeling
• Physical Chemistry

Background:

• United-atom (UA) models are crucial for simulating alkylamines.
• Existing models face challenges in accurately predicting thermodynamic and dielectric properties.
• Polarization effects are critical for accurate molecular simulations.

Purpose of the Study:

• To develop and validate a new UA model for alkylamines using the polarization consistent approach (PolCA).
• To improve the accuracy and transferability of UA models by incorporating post-facto polarization corrections.
• To assess the model's performance against experimental data and compare it with existing state-of-the-art models.

Main Methods:

• Development of a new UA model for alkylamines within the PolCA formalism.
• Application of post-facto polarization corrections.
• Parameterization against experimental density, enthalpy of vaporization, and dielectric constant.
• Validation using self-solvation and n-hexadecane solvation free energies.
• Estimation of liquid-phase amine dipole moments using Self-Consistent Electrostatic Embedding.

Main Results:

• The new PolCA model demonstrates superior performance compared to the GROMOS UA model.
• Systematic deviations in methylamine predictions observed with the GROMOS model are eliminated.
• Polarization energy corrections are essential for accurate simulations of mixtures with varying polarity.
• The model overestimates the dielectric constant for small amine molecules, indicating a higher effective dipole moment than experimentally observed in the liquid phase.

Conclusions:

• The developed PolCA model offers improved accuracy and transferability for simulating alkylamines.
• The study highlights the necessity of polarization corrections, especially when simulating mixtures.
• A key limitation identified is the overestimation of the dielectric constant for small amines, linked to effective dipole moments.