Force field simulation of guest induced gating phenomena

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The theoretical simulation of flexible switchable MOFs, especially with a high number of inner degrees of freedom, is still a difficult and untackled problem. Based on the complete first-principles parameterized MOF-FF model for the pillared layer MOFs synthesized in S1 and S2, molecular dynamics (MD) and grand canonical MD (GCMD) simulations will be performed in project T2 to investigate the structural transformation of such systems on a molecular level, stimulated by heat, pressure or guest molecule adsorption. In contrast to T1, the focus is more on the large length and timescales, however, with a close interaction to T1 in order to provide structural information for the electronic structure calculations, linking to the spectroscopic projects P1 and P2. The thermodynamic integration (TI) GCMD approach developed in the first funding period will be extended and validated with the final target to rationalize the separation of small hydrocarbons in fu-MOFs with functionalized flexible side chains at the linker (QP1, QF1). In a screening of a library of extended linkers and/or guest molecules (S2) with MD simulations, specific interactions determining the switchability will be identified (QP4), additionally serving as input for quantum mechanics calculations of spectroscopic properties by T1 (QP1). The methodical achievements of the first funding period will be exploited to simulate large size systems, allowing to study the formation of interfaces between different phases and the impact of surfaces (QP1&3). Primary targets are the thermal opening of nanoparticles (absence of periodic boundary conditions) and the adsorptive switching of 2D-periodic slabs (S1). A further step in size will be achieved by using coarse grained force fields developed in our group to investigate correlated phenomena during the structural transformation on an even larger size range (QP3). Finally, the novel GCMD methods will be applied for the simulation of liquid adsorption with short chain alcohols as solvent (studied in S2), which is notoriously difficult for standard GC Monte Carlo methods for such dense systems (QP1, QF2).