Coarse-grained modeling of zeolitic imidazolate framework-8 using MARTINI force fields

In this contribution, the well-known MARTINI particle-based coarse graining approach is tested for its ability to model the ZIF-8 metal-organic framework. Its capability to describe structure, lattice parameters, thermal expansion, elastic constants and amorphization is evaluated. Additionally, the less coarsened models were evaluated for reproducing the swing effect and the host-guest interaction energies were analyzed. We find that MARTINI force fields successfully capture the structure of the Metal-Organic Framework (MOF) for different degrees of coarsening, with the exception of the MARTINI 2.0 models for the less coarse mapping. MARTINI 2.0 models predict more accurate values of C11 and C12, while MARTINI 3.0 has a tendency to underestimate them. Among the possibilities tested, the choice of bead flavors within a particular MARTINI version appears to have a less critical impact in the simulated properties of the empty framework. None of the coarse-grained (CG) models investigated were able to capture the amorphization nor the swing effect within the scope of MD simulations. A perspective on the importance of having a proper Lennard-Jones (LJ) parametrization for modeling guest-MOF and MOF-MOF interactions is highlighted.