A QM/MM Derived Polarizable Water Model for Molecular Simulation.

Area of Science:

• Computational Chemistry
• Molecular Modeling
• Physical Chemistry

Background:

• Accurate simulation of condensed-phase systems requires reliable polarizable molecular models.
• Quantum Mechanics/Molecular Mechanics (QM/MM) methods offer a way to compute properties like polarizability.

Purpose of the Study:

• To propose an improved QM/MM strategy for determining condensed-phase polarizabilities.
• To optimize a new, simple, polarizable four-site water model for classical molecular simulations.

Main Methods:

• Developed a consensus-fitting strategy within QM/MM to reduce uncertainty in polarizability calculations.
• Fitted electrostatic, polarization, and dispersion properties using quantum and QM/MM calculations.
• Minimized model parameters by focusing on exchange repulsion for empirical calibration.

Main Results:

• The consensus-fitting strategy significantly reduces uncertainty in polarizability calculations, especially under small external electric fields.
• The optimized four-site water model accurately describes pure-liquid thermodynamic and transport properties.
• The approach successfully minimized the number of free parameters in the water model.

Conclusions:

• The proposed QM/MM strategy is effective for determining condensed-phase polarizabilities.
• The new polarizable water model demonstrates good performance for classical molecular simulations.
• Minimizing free model parameters through robust fitting strategies enhances model reliability.