Publication: An Ising model for metal-organic frameworks
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American Institute of Physics
We present a three-dimensional Ising model where lines of equal spins are frozen such that they form an ordered framework structure. The frame spins impose an external field on the rest of the spins (active spins). We demonstrate that this “porous Ising model” can be seen as a minimal model for condensation transitions of gas molecules in metal-organic frameworks. UsingMonte Carlo simulation techniques, we compare the phase behavior of a porous Ising model with that of a particle-based model for the condensation of methane (CH4) in the isoreticular metal-organic framework IRMOF- 16. For both models, we find a line of first-order phase transitions that end in a critical point. We show that the critical behavior in both cases belongs to the 3D Ising universality class, in contrast to other phase transitions in confinement such as capillary condensation.
© AIP Publishing. We thank Christoph Janiak for useful discussions. N.H. and J.H. acknowledge financial support by Strategischer Forschungsfonds (SFF) of the University of Düsseldorf in the framework of the PoroSys network and by the German DFG, FOR 1394 (Grant No. HO 2231/7-2). V.M.M. and B.S. were partially supported by MINECO (Spain) through Grant No. FIS2015-65078-C2-1-P. This project has received funding from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska Curie Grant Agreement No. 654971. Computer time at the ZIM of the University of Düsseldorf is also gratefully acknowledged.