Incorporating Flexibility Effects into Metal-Organic Framework Adsorption Simulations Using Different Models.

Area of Science:

• Computational Chemistry
• Materials Science
• Chemical Engineering

Background:

• High-throughput molecular simulations aid in identifying metal-organic frameworks (MOFs) for chemical separations and storage.
• Current computational methods typically approximate MOFs as rigid structures for simplicity.
• The impact of MOF flexibility on adsorption prediction accuracy remains largely unexplored.

Purpose of the Study:

• To evaluate the necessity of including metal-organic framework (MOF) flexibility in adsorption prediction simulations.
• To compare the accuracy of flexible MOF simulations against rigid approximations and approximate flexibility methods.
• To investigate potential correlations between MOF elastic properties and the significance of flexibility effects.

Main Methods:

• Extensive adsorption-relaxation simulations incorporating full MOF flexibility were performed.
• Four MOFs with established CO2 isotherms were used to benchmark flexibility models.
• Adsorption properties (Henry's constants, selectivity) for seven adsorbates in 15 MOFs were analyzed.

Main Results:

• Adsorption-relaxation simulations are crucial for quantitative adsorption predictions in many MOFs, particularly at dilute concentrations.
• Rigid structure calculations offer some insights but lack the accuracy of flexible simulations.
• No simple correlation was found between the elastic properties of empty MOFs and the importance of flexibility.

Conclusions:

• Accounting for metal-organic framework (MOF) flexibility is essential for accurate molecular adsorption predictions.
• Rigid framework approximations are often inadequate, necessitating more computationally intensive flexible simulations.
• Further research is needed to understand the interplay between MOF structure, elasticity, and adsorption behavior.