Density-Functionalized QM/MM Delivers Chemical Accuracy For Solvated Systems

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Quantum Mechanics/Molecular Mechanics (QM/MM) is a hybrid method combining quantum mechanics (QM) and molecular mechanics (MM).
• Accurate QM/MM simulations require consistent treatment of QM and MM subsystems and their interactions.
• Existing QM/MM methods face challenges in accurately describing the interface and ensuring consistency.

Purpose of the Study:

• To reformulate QM/MM as a fully quantum mechanical theory using density functional theory (DFT).
• To develop a method that treats both QM and MM subsystems at the DFT level, including their interactions.
• To achieve rapid convergence to chemical accuracy with increasing QM subsystem size.

Main Methods:

• Reformulation of QM/MM using density functional theory (DFT) for both QM and MM subsystems.
• Assignment of an ad hoc electron density for the MM subsystem and application of orbital-free DFT functionals.
• Treatment of QM/MM interactions using orbital-free density functionals, including Coulomb, exchange, correlation, and Pauli repulsion.
• Utilization of data-driven, many-body MM force fields for consistency with DFT functionals.

Main Results:

• Demonstrated unprecedented, very rapid convergence to chemical accuracy as the QM subsystem size increases.
• Successfully applied the method to various water-solvated systems.
• Validated the approach through pilot studies on water bulk, clusters, solvated glucose, a palladium aqua ion, and MoS2 monolayer.

Conclusions:

• The proposed QM/MM reformulation offers a robust and efficient fully quantum mechanical approach.
• The method shows significant promise for accurate simulations of complex chemical and material systems.
• This work advances the capability of DFT-based simulations for interacting QM/MM subsystems.