Efficient Free Energies from a Simplified Electrostatic Embedding QM/MM Approach Based on Electrostatic Potential...

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Molecular Modeling

Background:

• Accurate free energy calculations are crucial in chemistry and biology.
• Periodic boundary condition (PBC)-adapted quantum mechanics/molecular mechanics (QM/MM) methods require efficient electrostatic treatments for condensed-phase systems.

Purpose of the Study:

• To develop a robust and efficient QM/MM approach for free energy calculations under PBC.
• To enable accurate computation of solvation free energies and redox potentials using electrostatic embedding.

Main Methods:

• Developed a QM/MM approach using electrostatic potential fitted (ESPF) charge operators.
• Combined smooth particle-mesh Ewald summation for QM-MM electrostatics and Ewald pair potential for QM-QM interactions.
• Implemented thermodynamic integration (TI) with novel coupling parameters for solvation and redox potential calculations.

Main Results:

• The QM/MM method is compatible with ab initio DFT and semiempirical DFTB frameworks.
• Calculated solvation free energies and redox potentials for amino acid analogues and aromatic ketones in water.
• Achieved qualitative agreement between computed and experimental data.

Conclusions:

• The developed ESPF-based QM/MM method provides an efficient and robust framework for free energy calculations.
• This work facilitates routine free energy computations using electrostatic embedding QM/MM methodologies.
• The approach is suitable for both solvation and redox potential studies in condensed phases.