Metal-organic frameworks (MOFs) are promising for many applications including heterogeneous catalysis. Fully quantum chemical investigations of these systems are usually quite demanding in terms of computer time and computational resources; therefore, combined quantum mechanical and molecular mechanical (QM/MM) methods are desirable to investigate these systems. This will be especially important as we move into the era of more demanding simulations enabled by exascale computing; therefore, it is important to develop improved methods and software for QM/MM calculations. The treatment of the QM-MM boundary strongly affects the accuracy of QM/MM calculations and is especially challenging for the treatment of MOFs due to the presence of high atomic charges on the inorganic nodes. The difficulty of treating high electrostatic fields is exacerbated when the boundary between the QM fragment and the MM fragment must pass through a covalent bond, which is unavoidable in treating MOFs. For QM/MM calculations having covalent bonds cut by the QM-MM boundary, it has been proposed previously to use a scheme with system-specific tuned fluorine link atoms. Here, we propose a broadly parametrized scheme called bond-tuned link-atom scheme where the parameters of the tuned F link atoms depend only on the type of bond being cut. We confirm that the proposed bond-tuned link-atom scheme can be as accurate as the system-specific tuned-F link-atom scheme. In addition, the bond-tuned link atoms are very convenient and are especially well adapted for high-throughput QM/MM calculations. We are currently applying the bond-tuned link-atom scheme to catalytic MOF systems.

Combined quantum mechanical and molecular mechanical methods and software for metal-organic frameworks

2019 Spring National Meeting

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