Force matching and iterative Boltzmann inversion coarse grained force fields for ZIF-8

Area of Science:

• Computational materials science
• Chemical physics
• Materials chemistry

Background:

• Coarse-grained (CG) modeling of metal-organic frameworks (MOFs) is underdeveloped due to a lack of suitable CG force fields.
• Existing methods often struggle to accurately represent MOF properties and behaviors.

Purpose of the Study:

• To develop and evaluate novel iterative Boltzmann inversion and force matching (FM) CG force fields for ZIF-8.
• To compare the performance of these new force fields against existing MARTINI force fields.
• To assess the ability of CG force fields to reproduce ZIF-8's structure, elastic properties, thermal expansion, and the "swing effect" phase transition.

Main Methods:

• Iterative Boltzmann inversion and force matching (FM) were employed to generate CG force fields for ZIF-8 at three resolutions.
• The developed force fields were validated by comparing their predictions against experimental data and existing MARTINI force fields.
• Key properties evaluated include structural reproduction, elastic tensor, thermal expansion, and the "swing effect" upon guest molecule loading.

Main Results:

• All developed force fields demonstrated reasonable accuracy in reproducing the structure of ZIF-8.
• Analysis revealed challenges in accurately capturing elastic constants and volume expansion using CG models.
• Force matching force fields showed particular promise in depicting the "swing effect" phenomenon in ZIF-8.

Conclusions:

• This study presents the first application of iterative Boltzmann inversion and FM CG methods to model porous solids like MOFs.
• The developed force fields offer a promising avenue for simulating ZIF-8 and other MOFs at the CG level.
• Significant challenges remain in fitting CG force fields for porous materials, particularly for capturing subtle phase transitions and mechanical properties.