The right isotherms for the right reasons? Validation of generic force fields for prediction of methane adsorption in metal-organic frameworks

Abstract

In recent years, the use of computational tools to aid in the evaluation, understanding and design of advanced porous materials for gas storage and separation processes has become ever-more widespread. High-performance computing facilities have become more powerful and more accessible and molecular simulation of gas adsorption has become routine, often involving the use of a number of default and commonly-used parameters as a result. In this work, we consider the application of molecular simulation in one particular field of adsorption -the prediction of methane adsorption in metal-organic frameworks in the low-loading regime -and employ a range of computational techniques to evaluate the appropriateness of many commonly chosen simulation parameters to these systems. In addition to confirming the power of relatively simple generic force fields to quickly and accurately predict methane adsorption isotherms in a range of MOFs, we demonstrate that these force fields are capable of providing detailed molecular-level information which is in very good agreement with quantum chemical predictions. We highlight a number of chemical systems in which molecular-level insight from generic force fields should be approached with a degree of caution and provide some general recommendations for best-practice in simulations of CH4 adsorption in MOFs.

Methane Adsorption in Zr-Based MOFs: Comparison and Critical Evaluation of Force Fields

“…In another recent study, it was concluded that generic force fields are suitable for the qualitative prediction of methane adsorption in MOFs in the low-loading regime. 19 In the same paper, it is demonstrated that these force fields are capable of providing detailed molecular-level information, although in some systems such conclusions should be approached with caution.…”

Role of particle size and surface functionalisation on the flexibility behaviour of switchable metal–organic framework DUT-8(Ni)

“…A cut-off radius of 18Å was used for all interactions which is large enough to ensure that the cut-off radius does not inuence the results while using the truncated LJ 12-6 potential. 55 DUT-8(Ni) partial atomic charges were taken as the Mulliken charges from DFT minimized structures. LJ parameters for the framework were taken from the Dreiding force eld, 56 with the exception of nickel, for which the parameters were taken from the Universal Force Field.…”

Simulation-based evaluation of zeolite adsorbents for the removal of emerging contaminants

“…71 The cutoff of 10 Å is smaller than values commonly used in simulations of gas adsorption isotherms (12.5 or 15 Å are more typical). 72 In this regard, it should be emphasised that it is the main aim of the MC simulations to generate low-energy configurations, which are then optimised using a cutoff of 12.5 Å for vdW interactions (see below). With this purpose in mind, it appears reasonable to limit the cutoff distance, as usage of a larger value is unlikely to shift the energetic ordering of different configurations.…”