An automated protocol to construct flexibility parameters for classical forcefields: applications to metal-organic...

Area of Science:

• Materials Science
• Computational Chemistry
• Condensed Matter Physics

Background:

• Force fields are crucial for simulating material properties.
• Accurate parameterization of flexibility is essential for metal-organic frameworks (MOFs).
• Existing methods often struggle with the complexity and redundancy of MOF flexibility interactions.

Purpose of the Study:

• To construct and validate robust forcefield flexibility parameters for a large dataset of MOFs.
• To develop a systematic protocol for identifying and quantifying important flexibility interactions in MOFs.
• To enable accurate molecular dynamics simulations of MOF properties.

Main Methods:

• Atom typing to identify bond, angle, and dihedral types.
• Pruning dihedral types to reduce redundancy while preserving symmetry.
• Classification of dihedral types (non-rotatable, hindered, rotatable, linear).
• Smart selection of important torsion modes.
• LASSO regression for computing force constants from quantum mechanically computed data (DFT, AIMD, torsion scans).
• Validation using independent datasets and calculating R-squared and RMSE.

Main Results:

• Developed and validated forcefield flexibility parameters for over 100 MOFs.
• Achieved high accuracy with average R-squared values of 0.910 ± 0.018 for atom-in-material forces on validation datasets, even without bond-bond cross terms.
• The SAVESTEPS protocol effectively parameterizes flexible forcefields.
• Successfully computed heat capacities and thermal expansion coefficients for two MOFs using the developed parameters.

Conclusions:

• The developed forcefield flexibility parameters and the SAVESTEPS protocol offer a reliable method for MOF simulations.
• The approach significantly advances the accurate computational modeling of MOF properties.
• This work paves the way for broader applications in materials design and discovery.