Polarizable Embedding with a Transferable H₂O Potential Function I: Formulation and Tests on Dimer.

Area of Science:

• Computational Chemistry
• Multiscale Modeling
• Quantum Mechanics/Molecular Mechanics (QM/MM)

Background:

• Accurate multiscale simulations require accounting for mutual polarization between different theoretical levels.
• Existing electrostatic embedding QM/MM models using point-charge force fields have limitations.

Purpose of the Study:

• To develop and present an energy functional for a QM/MM scheme incorporating reciprocal polarization.
• To improve the accuracy of QM/MM simulations for electronic excitations and charge transfer processes.

Main Methods:

• Coupling density functional theory (DFT) for the QM subsystem with a single-center multipole expansion (SCME) for the molecular mechanics (MM) subsystem.
• The SCME description includes anisotropic dipole and quadrupole polarizability and static multipoles up to the hexadecapole.
• The energy functional and coupling scheme are general and extendable to higher-order moments.

Main Results:

• The developed QM/MM method with reciprocal polarization alleviates shortcomings of point-charge based models.
• Tests on a water dimer show QM/MM results falling between pure DFT and pure SCME values.
• Consistency of many-body energy contributions and analytical forces was demonstrated for a water pentamer.

Conclusions:

• The presented QM/MM energy functional with reciprocal polarization offers a more accurate approach for multiscale simulations.
• This method provides a robust framework for studying complex chemical systems involving electronic phenomena.
• The approach is general and can be extended to more complex systems and higher-order polarization effects.