Abstract
AbstractThe displacive phase transformation of metal‐organic frameworks (MOFs), referred to as “breathing,” is computationally investigated intensively within periodic boundary conditions (PBC). In contrast, the first‐principles parameterized force field MOF‐FF is used to investigate the thermal‐ and pressure‐induced transformations for non‐periodic nanocrystallites of DMOF‐1 (Zn2(bdc)2(dabco); bdc: 1,4‐benzenedicarboxylate; dabco: 1,4‐diazabicyclo[2.2.2]octane) as a model system to investigate the effect of the PBC approximation on the systems' kinetics and thermodynamics and to assess whether size effects can be captured by this kind of simulation. By the heating of differently sized closed pore nanocrystallites, a spontaneous opening is observed with an interface between the closed and open pore phase moving rapidly through the system. The nucleation temperature for the opening transition rises with size. By enforcing the phase transition with a distance restraint, the free energy can be quantified via umbrella sampling. The apparent barrier is substantially lower than for a concerted process under PBC. Interestingly, the barrier reduces with the size of the nanocrystallite, indicating a hindering surface effect. The results demonstrate that the actual free energy barriers and the importance of surface effects for the transformation under real conditions can only be studied beyond PBC.
Highlights
Such structural transformations, which can periodic boundary conditions (PBC)
Since Ewald type calculations of the Coulombic interactions are prohibitive for the non-periodic NC simulations, we first tested the use of cutoff based schemes
We have performed the first simulations of a breathing phase transformation for nanocrystallite models of the pillared layer DMOF-1 beyond periodic boundary conditions, using the first principles parameterized force field moderate loading of guest frameworks (MOFs)-FF
Summary
Such structural transformations, which can periodic boundary conditions (PBC). In contrast, the first-principles lead to hysteretic behavior and gate openparameterized force field MOF-FF is used to investigate the thermal- and pressure-induced transformations for non-periodic nanocrystallites of DMOF-1 (Zn2(bdc)2(dabco); bdc: 1,4-benzenedicarboxylate; dabco: ing upon guest adsorption, can have enormous impact for the applicability of MOFs in gas adsorption,[5] gas separation, and other potential applications such as. In particular the MIL-53 series was most intenfree energy barriers and the importance of surface effects for the sively investigated both experimentally and transformation under real conditions can only be studied beyond PBC. Most systems are symmetric with respect can undergo structural transformations (upon certain stimuli to two directions and the shear displacement can occur in eilike, e.g., guest adsorption) as third generation soft porous ther direction. For MIL-53 the system is in the op crsytals.[1] The so-called “breathing” effect, where metal-organic form when activated and closes for moderate loading of guest frameworks (MOFs) show large volume changes, is one of the molecules like CO2 which interact strongly with the inorganic rod like structures.[19] At higher loading the system opens up into. The entropy contributions gain weight and favor the op form, whereas hydrostatic pressure leads to a transformation to the cp form.[11,18]
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