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Effect of Partial Charge Calculation Method on Adsorption Thermodynamics in Metal-organic Frameworks

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Depiction of interactions of carbon dioxide with a porous adsorbent. Credit: NIST.

In classical molecular simulations, electrostatic contributions to the potential energy are typically accounted for by assigning partial charges to some or all atoms in the system.

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Summary

The adsorption properties obtained by simulation then serve as a qualitative measure of the variability that may follow from the choice of partial charge calculation method. Electrostatic interactions are an important contribution to the interatomic or intermolecular potential energy in any system, whether homogeneous (bulk phase) or heterogeneous (fluid and confining material or multiple fluid phases). Such ab initio methods may be incorporated into molecular simulations to model complex systems, e.g., the Car-Parrinello Molecular Dynamics method, though at high computational cost. For crystalline materials, such as metal-organic frameworks (MOF), partial charges are often computed from ab initio calculations of some prescribed method. Even for a particular MOF, there is often great variation between the charges computed by two methods.

Thus far, they have computed partial charges for a variety of popular MOFs, including ZIF-8 and some from the IRMOF family, using density functional theory and several partial charge methods. This site provides electronic structure and thermophysical properties data computed using quantum mechanical and molecular simulation techniques and compiled by NIST under the Standards Reference Data Program.

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