Incorporating Material Flexibility Effects into Adsorption Modeling Using Nonlocal Density Functional Theory

Area of Science:

• Materials Science
• Computational Chemistry
• Chemical Engineering

Background:

• Conventional density functional theory (cDFT) models often assume rigid porous materials, limiting their application to flexible frameworks.
• Understanding fluid adsorption in deformable materials is crucial for applications like gas storage and separation.

Purpose of the Study:

• To develop a thermodynamically consistent framework for modeling adsorption in flexible nanoporous materials.
• To overcome the limitations of rigid-host assumptions in existing cDFT models.

Main Methods:

• Coupling three-dimensional classical density functional theory (cDFT) with the SAFT-VR-Mie equation of state and the osmotic ensemble formalism.
• Validating the framework on a MIL-53-type model and applying it to methane adsorption in MIL-53.

Main Results:

• The model accurately reproduces adsorption isotherms and grand potential trends compared to molecular simulations.
• It captures adsorption-induced structural transitions and breathing phenomena in flexible metal-organic frameworks.
• The framework shows good agreement with experimental data for methane adsorption in MIL-53.

Conclusions:

• The developed osmotic SAFT-cDFT approach provides a computationally efficient tool for studying adsorption-deformation coupling in responsive porous materials.
• It offers insights into the mechanisms of breathing transitions and hysteresis in flexible frameworks.
• The framework opens new avenues for screening and thermodynamic analysis of flexible metal-organic frameworks.