Partial hessian fitting for determining force constant parameters in molecular mechanics

Area of Science:

• Computational Chemistry
• Materials Science

Background:

• Molecular mechanics (MM) force fields are crucial for simulating molecular systems.
• Accurate force constant parameters are essential for reliable MM simulations.
• Existing methods for parameter derivation can be computationally intensive or less accurate.

Purpose of the Study:

• To introduce a novel, efficient, and accurate protocol for deriving force constant parameters for MM force fields.
• To improve the accuracy of MM simulations, particularly for systems with soft bonds.
• To develop parameters suitable for AMBER-type energy expressions.

Main Methods:

• A new protocol called partial Hessian fitting (PHF) was developed.
• A 3x3 partial matrix from the MM Hessian is fitted to the QM-computed Hessian.
• The fitting is performed analytically in a least-squares sense for rapid parameter derivation.
• The Katachi procedure was introduced to refine parameters for soft bonds.

Main Results:

• The PHF method successfully derived force constant parameters for AMBER-type energy expressions.
• Test calculations demonstrated that PHF parameter sets accurately reproduce QM-calculated frequencies.
• The Katachi procedure effectively resolved significant deviations in MM-optimized geometries for molecules with soft bonds.

Conclusions:

• The PHF protocol offers a rapid and accurate approach for deriving MM force field parameters.
• The developed parameters show good performance in reproducing QM data.
• The Katachi procedure enhances the accuracy of MM simulations for complex molecules, including those in metal-organic frameworks.