Perspective from a Hubbard U-density corrected scheme towards a spin crossover-mediated change in gas affinity

Area of Science:

• Computational materials science
• Chemical physics
• Solid-state chemistry

Background:

• Spin crossover (SCO) materials offer tunable properties based on their spin state.
• Gas release mechanisms in SCO materials are not fully understood.
• Designing materials for selective gas adsorption and release is crucial for various applications.

Purpose of the Study:

• To provide design principles for materials exhibiting spin crossover-assisted gas release.
• To elucidate the mechanisms governing changes in gas binding energy upon spin transitions.
• To assess the feasibility of these mechanisms in porous crystalline structures.

Main Methods:

• Density functional theory (DFT) with a Hubbard U density-corrected scheme.
• Case studies using small molecular fragments to understand binding energy changes.
• Correlation of gas binding energy changes with spin state transitions in Hofmann-type clathrates (Fe, Mn, Ni).

Main Results:

• Two primary mechanisms for binding energy changes during spin transitions were identified.
• Feasibility in porous crystals was assessed for CO2, CO, N2, and H2 adsorption.
• Promising cases for N2 and H2 adsorption were found, with H2 showing a particularly large binding energy change due to a Kubas mechanism.

Conclusions:

• The study provides a general perspective for engineering open-metal site frameworks with tailored local environments.
• Materials can be designed to exhibit spin crossover upon adsorption of specific gas molecules.
• This approach facilitates the development of advanced materials for gas storage and separation.