Free energy landscapes for the thermodynamic understanding of adsorption-induced deformations and structural transitions in porous materials

Abstract

Soft porous crystals are flexible metal-organic frameworks that respond to physical stimuli such as temperature, pressure, and gas adsorption by large changes in their structure and unit cell volume. While they have attracted a lot of interest, molecular simulation methods that directly couple adsorption and large structural deformations in an efficient manner are still lacking. We propose here a new Monte Carlo simulation method based on non-Boltzmann sampling in (guest loading, volume) space using the Wang-Landau algorithm, and show that it can be used to fully characterize the adsorption properties and the material's response to adsorption at thermodynamic equilibrium. We showcase this new method on a simple model of the MIL-53 family of breathing materials, demonstrating its potential and contrasting it with the pitfalls of direct, Boltzmann simulations. We furthermore propose an explanation for the hysteretic nature of adsorption in terms of free energy barriers between the two metastable host phases.

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• The Behavior of Flexible MIL-53(Al) upon CH4 and CO2 Adsorption
• Understanding and Improving the Wang-Landau Algorithm
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Cited by in corpus (4)

• Computational characterization and prediction of metal-organic framework properties
• Water Adsorption in Soft and Heterogeneous Nanopores
• Challenges in first-principles NPT molecular dynamics of soft porous crystals: A case study on MIL-53(Ga)
• Elastic heterogeneity governs asymmetric adsorption-desorption in a soft porous crystal