Ab Initio Flexible Force Field for Metal–Organic Frameworks Using Dummy Model Coordination Bonds

Abstract

We present force fields developed from periodic density functional theory (DFT) calculations that can be used in classical molecular simulations to model M-MOF-74 (M = Co, Fe, Mg, Mn, Ni, Zn) and its extended linker analogs. Our force fields are based on cationic dummy models (CDMs). These dummy models simplify the methodology required to tune the parameters and improve the accuracy of the force fields. We have used our force fields to compare mechanical properties across the M-MOF-74 series, and determine that increasing the size of the linker decreases the framework rigidity. In addition, we have applied our force fields to an extended linker analog of Mg-MOF-74 and characterized the free energy of previously-reported deformation pattern, in which the one-dimensional hexagonal channels of the framework become irregular. The free energy profiles confirm that the deformation is adsorbate-induced and impossible to access solely by a pressure stimulus. Based on our results, we conclude that the force fields presented here and others that may be developed using our methodology are transferable across metal-organic framework series that share a metal center topology. Finally, we believe that these force fields have the potential to be adapted for the study of complex problems in MOF chemistry, including defects and crystal growth, that have thus far been beyond the scope of classical molecular simulations.

Preserving Porosity of Mesoporous Metal–Organic Frameworks through the Introduction of Polymer Guests

“…In order to better understand the physical origins of the structural collapse of M 2 (NDISA), we used a recently developed model for M 2 (dobdc) analogues to perform simulations of the framework. 50 This model was previously tested successfully on a series of isoreticular M 2 (dobdc) analogues that are known to be stable upon activation. This series included IRMOF-74-V, which has a structure similar to M 2 (NDISA), but slightly larger pores (38 Å).…”

“…Metal−metal and metal−oxygen interactions are taken from a model for M 2 (dobdc) analogues. 50 Geometric mixing rules are used to combine DREIDING Lennard-Jones parameters for carbon and hydrogen with the M 2 (dobdc) model-based metal−metal interactions to compute the nonbonded metal−carbon and metal−hydrogen interactions. Nonbonded and short-range electrostatic interactions were truncated at 12.5 Å, and Ewald summations were used to calculate long-range electrostatic interactions.…”

“…The force field correctly found the ground state configuration of the ligand. Metal–metal and metal–oxygen interactions are taken from a model for M 2 (dobdc) analogues . Geometric mixing rules are used to combine DREIDING Lennard-Jones parameters for carbon and hydrogen with the M 2 (dobdc) model-based metal–metal interactions to compute the nonbonded metal–carbon and metal–hydrogen interactions.…”

Design principles for the ultimate gas deliverable capacity material: nonporous to porous deformations without volume change

“…Force field information and GCMC settings are provided in S2.2. 39,40,60 How, and at what pressure, any S-shaped adsorption profile occurs will clearly depend on the underlying framework and framework-guest potential energy surface, although we are unaware of any specialized MOF force fields [61][62][63][64] designed specifically for this Sr coordination environment that also capture the non-bonded interactions between methane and the open metal site. [65][66][67][68] Nonetheless, the true isotherm will be bounded between the F| DFT F and F| DFT F•8CH 4 isotherms.…”

Parametrization of Non-Bonded Force Field Terms for Metal-Organic Frameworks Using Machine Learning Approach

“…[61,62,63] Extended versions of UFF [64,65] and more specialized FFs [66,67] have also been proposed. Ab initio derived [68,69,70] and explicitly polarizable [71,72,73] FFs help to significantly improve the description of intermolecular interactions only for small series of isoreticular structures, leaving the aforementioned dilemma largely unaddressed. Therefore, to facilitate HTS adsorption studies, it is necessary to develop a fast automatized procedure for the generation of FF components, which will be suitable for various atomic types presented in MOFs.…”