Polarizable Embedding with a Transferable H₂O Potential Function II: Application to (H₂O) Clusters and Liquid Water

Area of Science:

• Computational Chemistry
• Molecular Dynamics
• Quantum Mechanics

Background:

• Accurate molecular simulations require incorporating polarization effects, especially for systems involving charge transfer.
• Existing multiscale quantum-mechanics/molecular-mechanics (QM/MM) methods often neglect polarization in the molecular mechanics (MM) region, limiting their applicability.

Purpose of the Study:

• To develop and validate a novel QM/MM formalism that includes dipole and quadrupole polarizability for the MM region.
• To assess the impact of polarizable embedding on the simulation of water molecules and liquid water structure.

Main Methods:

• A recently developed QM/MM formalism was employed, utilizing density functional theory for the QM region.
• The MM region employed a potential energy function for H2O molecules that included quadrupole and dipole polarizability.
• Simulations were performed for liquid water and various water clusters.

Main Results:

• The QM/MM binding energies for water clusters showed minimal deviation (within 20 meV/molecule) compared to single-model results.
• Interaction energy differences were not systematically correlated with induced MM moments from the polarizable embedding scheme.
• Optimized hexamer geometries and liquid water structure were significantly improved compared to models neglecting polarization.

Conclusions:

• The developed polarizable QM/MM method accurately captures polarization effects in water simulations.
• This approach offers improved structural and energetic predictions for water systems compared to non-polarizable models.
• The findings highlight the importance of including polarization in QM/MM simulations for accurate molecular modeling.