Modeling the structural and thermal properties of loaded metal-organic frameworks. An interplay of quantum and anharmonic fluctuations

Abstract

Metal-organic frameworks show both fundamental interest and great promise for applications in adsorption-based technologies, such as the separation and storage of gases. The flexibility and complexity of the molecular scaffold poses a considerable challenge to atomistic modeling, especially when also considering the presence of guest molecules. We investigate the role played by quantum and anharmonic fluctuations in the archetypical case of MOF-5, comparing the material at various levels of methane loading. Accurate path integral simulations of such effects are made affordable by the introduction of an accelerated simulation scheme and the use of an optimized force field based on first-principles reference calculations. We find that the level of statistical treatment that is required for predictive modeling depends significantly on the property of interest. The thermal properties of the lattice are generally well described by a quantum harmonic treatment, with the adsorbate behaving in a classical but strongly anharmonic manner. The heat capacity of the loaded framework - which plays an important role in the characterization of the framework and in determining its stability to thermal fluctuations during adsorption/desorption cycles - requires, however, a full quantum and anharmonic treatment, either by path integral methods or by a simple but approximate scheme. We also present molecular-level insight into the nanoscopic interactions contributing to the material's properties and suggest design principles to optimize them

References in corpus (17)

• A real-space grid implementation of the Projector Augmented Wave method
• Competing quantum effects in the dynamics of a flexible water model
• Nuclear quantum effects enter the mainstream
• Accurate sampling using Langevin dynamics
• Isothermal-isobaric molecular dynamics using stochastic velocity rescaling
• Efficient stochastic thermostatting of path integral molecular dynamics
• i-PI 2.0: A Universal Force Engine for Advanced Molecular Simulations
• Minimal Basis Iterative Stockholder: Atoms in Molecules for Force-Field Development
• i-PI: A Python interface for ab initio path integral molecular dynamics simulations
• Robust and efficient configurational molecular sampling via Langevin Dynamics
• Efficient first-principles calculation of the quantum kinetic energy and momentum distribution of nuclei
• Accurate molecular dynamics and nuclear quantum effects at low cost by multiple steps in real and imaginary time: using density functional theory to accelerate wavefunction methods
• Controlling Thermal Expansion: a Metal Organic Frameworks Route
• High Order Path Integrals Made Easy
• Equation of state of fluid methane from first principles with machine learning potentials
• Path integral virial estimator based on the scaling of fluctuation coordinates: Application to quantum clusters with fourth-order propagators
• The inefficiency of re-weighted sampling and the curse of system size in high order path integration

Cited by in corpus (6)

• A complete description of thermodynamic stabilities of molecular crystals
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• i-PI 3.0: a flexible and efficient framework for advanced atomistic simulations
• Quantum dynamics using path integral coarse-graining
• Progress and Challenges in Ab Initio Simulations of Quantum Nuclei in Weakly Bonded Systems
• The importance of nuclear quantum effects for NMR crystallography