Effective yet reliable computation of hyperfine coupling constants in solution by a QM/MM approach: Interplay between...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Quantum Mechanical/Molecular Mechanics (QM/MM) methods are crucial for studying complex molecular systems.
• Accurately modeling Pauli repulsion and dispersion effects is essential for precise QM/MM calculations.
• Existing QM/MM models often lack explicit inclusion of repulsion and dispersion in the QM Hamiltonian.

Purpose of the Study:

• To extend existing QM/MM models to include Pauli repulsion and dispersion effects for hyperfine coupling constant calculations.
• To develop a novel parametrization for electrostatic fluctuating charge force fields.
• To quantitatively reproduce reference QM interaction energies and predict Electron Paramagnetic Resonance (EPR) parameters.

Main Methods:

• Extension of a previously proposed QM/MM model to explicitly include repulsion and dispersion terms in the QM Hamiltonian.
• Development and novel parametrization of an electrostatic fluctuating charge force field.
• Testing the approach against the prediction of EPR parameters for nitroxide radicals in aqueous solutions.

Main Results:

• The proposed QM/MM approach successfully incorporates Pauli repulsion and dispersion effects directly into the QM Hamiltonian.
• A new parametrization of the electrostatic fluctuating charge force field allows for quantitative reproduction of QM interaction energies.
• The model accurately predicts EPR parameters of nitroxide radicals, validating its efficacy.

Conclusions:

• The developed QM/MM method provides a more accurate framework for calculating hyperfine coupling constants by including crucial repulsion and dispersion effects.
• The novel force field parametrization enhances the reliability of QM/MM simulations for energetic and spectral properties.
• This approach offers a significant advancement for computational studies of molecular properties and spectra, particularly for radical species.